How far can you go with a desktop CNC machine?

I'm a hobbyist with a half dozen or so builds and dozens of accessories under my belt. All of which I've been able to do thanks to the giants in this community who share their files and make this all so easy.

My question is twofold, and is born out of ignorance of the requirements of machined metal parts, as well as the capabilities of CNC machines.

If you had a simple desktop CNC machine, like a Carvera or whatever would be the Ender3 equivalent, how much of an AR15 build, for example, could you go? I remember seeing some chatter about people subtracting lower receivers using machines like this, but could you go farther and make a BCG, a barrel, a buffer tube, or any of the components of the FCG?

What about for builds like a Mac 11? It seems like the parts kits sellers are machining those themselves.

And for a glock, it seems like the rails you could make very quickly, but could you make a barrel or a slide?

Lastly, aside from the mechanical capabilities of the machine, theres the question of access for people like me who currently have no confidence in designing files safe for use. I haven't seen any CNC ready files in my browsing on the Index, which I take is due to the rarity of CNC machines amongst the community. Would it be safe to assume that once word gets out in the community that there's a sub $1,000 CNC machine that lets you go farther on your builds than just a 3DP, that we'd see a proliferation of CNC ready files?