I don't know about Nvidia drivers, but the 'core' radeon* runs about ~150 MB and there's a bunch of non-drivery cruft that looks pretty -ish, and makes tweaking various settings slightly more convenient and crashy.

*which I haven't updated in a couple of years since it works fine

You'll no doubt find that the .inf file that is the actual driver is very small, and is really all that's needed for displaying an image and dual screening. It's all the other gubbins when it comes to acceleration and trying to provide you an 'experience'. I got a new Radeon card last year and thought that I'd install all the game aware software that comes with it to, in theory, make things easier by having tweaked profiles for each game. Turns out it's utter shite, caused problems in running many games - Doom 2016 for instance crashed after 10 minutes of play time - and it was all because the Radeon suite was installed. Some of the per game settings in it were less than necessary; I don't really care to alter the voltage settings of my card for any particular game, it's a level of detail I have no appreciation of. 

Once it was uninstalled things have been running much better, but it inflated the install of the drivers to around ~350MB. So, yeah, its not unusual nowadays for the installs to be that big, but if you can do without the extras, I'd recommend moving them to the recycle bin. 
 

Most of the updates are for cards and games I don't even own, even though in theory they would still work with my card & games ok.

The binary drivers are of similar size. The open sores ones are more compact, but don't access the fancier acceleration functions for games etc. IIRC the nvidia open source are barely functional. I do use them on a work pc for a pretty low-end card, and they seem ok for everyday desktop stuff.

The proprietary drivers are definitely smaller on Linux (~33mb on disk on my system) but that's largely because the Windows drivers contain a shitload of what are essentially runtime-patches for games. A lot of stuff, particularly shaders, in games is poorly coded and nvidia essentially rewrite them, stick them in the drivers, then replace them in the game when it runs. Everyone wins - the games run better and nvidia cards look good. These take up a *lot* of space.

They don't bother porting that stuff to Linux.

 

I haven't installed binary drivers for linux in >10 years, they weren't worth the bother. Although they had better 3d acceleration, 2d for typical desktop stuff was kind of sucky.

Some distros make a meal of them for some reason. On Arch it's as much bother as typing `pacman -S nvidia`.

And how many shaders does Pacman require?

Over 7.

Installing is easy.

Good gravy.  :-O