Yep disk space and learning curve are the two major downsides to Nix. The former has never been a problem for me in practice, just run garbage collection once a month. The latter was a big problem, but is now mitigated for most people by LLMs.

Yes, however the space is not „used up” in a classic sense. It’s a cache, so you can give up some of it and reclaim your space. Fresh after a full cleanup it won’t take much more than a regular distro.

Yes. But disk space isn't exactly the most valuable resource you have as a developer/power user

actually once I garbage collect, nixos actually uses up less disk space for me than other distros

Use nix.optimise.automatic = true in the config and perform nix-collect-garbage if necessary. With this it doesn't take much.