It’s a different use case - bottles is really good for playing games outside of steam (like pirated titles or non-steam games) since it has sandboxing + you just drag and drop the game folder, then add executable as shortcut and run without having to fiddle with paths and set up each game individually. Convenient for software too that runs better on proton too.

If you don’t do/have a need for any of that, then you don’t need bottles.

I like them as an option, there are some programs like Bottles or specific game launchers that work under flatpak better than the versions available via native package manager (with Bottles in particular, you can use various built-in sandbox features via flatpak which makes things a bit more secure), but it’s also a bit of a pain because it’s an additional package manager you have to update separately now, or tweak if things go wrong.

Fitgirl is a repacker, not a cracker so this really depends what kind of a release is it, so you’d have to test by yourself.

It should work when it comes to launching the game, I’ve done it before in the past. But in theory, it’s unlikely to work with achievements given how cracks tend to overwrite the steam api dll files and hooks, likely disabling achievements in the process as part of the crack.

Something you could try is to copy the steam dll files like steam_api64.dll from the original copy on steam to the cracked one and see if that does the trick.