can you use blender without addons, yes but after using blender for a while you will start to realize how difficult it is to do some basic stuff.
Example 1: keyframe multiple objects
open blender and try setting keyframe animation for multiple objects at once, you can do this for basic things like rotation, scale and location by pressing I, but for more complicated things, like properties you can’t. one possible way is using ctl+L to link animation data but that means all animation data will be copied and linked to the other objects, any changes you make to one object will affect the other objects it gets frustrating really quickly, alternatively an addon like key selected objects adds that functionality easily.
Example 2: keyframe offset
if you have ever worked in other animation software like after effects or cinema 4d, you may be used to certain features that you would automatically expect to exist in blender but they dont, like keyframe offset, in after effects and cinema 4d, you can easily offset the animation of different selected objects, this makes motion graphics way easier to make, unfortunately a feature like that does not exist in blender, but its really easy to implement if you know some python which is what i did for my addon quick functions. i just scripted the basic functionality and added it into a button in by addon, i can offset keyframes linearly, randomly or in reverse.
Example 3: Doing the Impossible
some addons simply do the impossible like wparallax, it introduces a totally new feature that is not built into blender, parallax shading is common in game engines like unreal and adds depth and detail to what would otherwise be flat surfaces, we all know how much time it would take you to model a single interior like this, but when using parallax shading you can easily fake it, an addon like this is a must for architectural visualization and rendering busy cities.
Example 4: the hobbyist vs the professional
sometimes its hard to see the value of an addon if you are just using blender as a hobby, for example the uv tools in blender are good enough for just about any object you want to unwrap, and it can be difficult to justify getting an addon like zenUv for most hobbyist, but if you make models professionally where you have to properly uv unwrap objects to industry requirements, then the inbuilt uv tools wont be enough, Zen uv brings tools like align, stack and unstack islands, relax uvs, create trim sheets and a lot of other features that are expected to be supported in a uv system that blender does not come with.
Example 5: do it the hard way
In most cases you can do everything without addons but that is usually doing things the hardway, anyone who has tried baking in blender knows what am talking about, lets say you are baking, a color map, a roughness map, ambient occlusion map, metalness and a normal map.
in substance painter you can just press one button and its done, but in blender you have to setup each map differently, create a new image, bake it and save it, hopefully you dont save it over other images you baked already otherwise you will have to repeat the whole process again and if you are trying to bake metalness it wont work, this is where addons help, they simplify complicated processes like this, in this case the simple bake addon has become my best recommendation for texture baking in blender.
Example 6: The community is faster
my first time coming across node previews like this, was when i was working in substance designer, each node shows you a small preview of what it does or generates, and when you combine different nodes you can see the results at all stages taking away the guesswork we have to do when working.
the moment i saw this in substance designer all i could think of is why dont we have something like this in blender, but i guess google was listening to my thoughts on that same day i saw a video about node preview on my youtube page as a brand new addon that introduces the same feature in blender a testament to fast the blender community is, features that would take too long to implement by the blender development team are implemented by the community.
Example 7: Not the same thing.
we need a way to differentiate addons, calling everything addons is miss leading, take an example of polyhaven asset browser, its more of a content library than an addon, it adds no new functionality to blender but brings a turn of value and content, this is what i call a content library, you maybe able to use blender without addons but using it without any content library like this is just throwing away time, alot of blender user hate using addons because they want to learn how to do things on their own, but after learning you need to get productive and content libraries are the best way to do it.
Example 8: More for less
polyhaven is just one of many content libraries, another useful one is sanctus library, this though is a mix of an addon and a content library as all of its assets rely on the addon and the addon rely on the assets to work, you are not just dragging the objects from the library into your viewport, you need the addon to access some functionality.
other content libraries that rely on addons they come with are geo scatter, great for scattering vegetation and objects, but you need objects and vegetation to scatter so the addon comes with its library of plants, grass, trees, stones to scatter.
Example 9: Lego Blocks
we all know what lego blocks are, its a bunch of plastic blocks that can be put together in unlimited ways to make anything you want, that’s what blender is, it has operators, it has modifiers, it has python scripts, tools, render engines, simulation systems and the list goes on an on, the blender team put all these thing together to make the blender we know and love, but that was just one way to assemble these tool, addons just reassemble these tools in a different way to make new functionality, a good example is conform object, they use already built-in tools like the subdivision modifier, a lattice, and a touch of python scripting to simplify how you wrap objects onto others.
Example 10: A better way
if you follow two minute papers then you know that all 3d applications like blender, maya, cinem4d and others don’t write every line of code in there program, all functionality, all tools start as a research paper that is latter implemented in your favorite software.
like manta flow, what blender uses for fluids and smoke simulation, it started as a technical paper presented at SIGGRAPH in 2016.
the whole bullet physics engine that blender uses for rigid body simulation is open sourced from github.
because all of this code is available to the public, sometimes blender artists think of better ways to implement it in blender different from how its done officially by the blender team, case in point Flip Fluids, which uses its own fluids solver to bring better fluid simulation in blender.
Example 11: Its A professional tool.
blender is slowly becoming a professional tool, and like other professional tools, they become more and more technical on every update, slowly removing obvious tools, like the Render image and render Animation button in blender 2.5 and below, while there is still a hair system in blender, its being fazed out in favor of using geometry nodes for hair, its seems the particle system will have the same fate too and so will other tools, professional tools provide a base starting point and building blocks for you to make your own tools, that is why houdini is so hard to use, same reason why some tools in blender are also hard to use, like the cloth tool, its easy to make cloth fall on other objects, but try to make a shirt or a dress, or a trouser.
the cloth simulation tool is just a starting point and you have to build the tools to help you use it more efficiently and those tools are what we call addons, addons like simply cloth.
so to answer the original question, can you use blender without addons, yes but its going to get harder and harder on each update, when new features are added to blender this means there are going to be less time to work on new tools for these features, so you will see fewer buttons and everything will become more technical because developers are working on new features and do not have time to add new buttons and tools that do basic things, like a button that sews clothes, the functionality is there but the button to easily do it is not there, like offsetting keyframes or setting keyframes for multiple objects, or pressing a button to render.
its going to get harder to use blender without addons as blender gets better.