EA App works great with Bottles. I haven't tried Ubisoft Connect myself, but the website says it works on a "gold" level - so might have some problems.
Well, these launchers can be a bit confusing at first, but you will get used to all that. And if you still have questions, that's what the community is here for.
I don't think that's distro related. I've played GW2 on Mint with an Nvidia card and it worked just like on Windows. I installed the Steam version though and linked my account.
What Proton version are you using in Steam to play it, did you try some different ones? Without knowing what your issue really is, there are some tinker steps mentioned on ProtonDB, maybe have a look. It's really hard to recommend anything without more info.
Boot times - I have an old and weak laptop, but it still works fine for some purposes. Boot times are so much shorter with Linux and I don't sit around waiting anymore :)
KeepassXC is great, but I realised very late in the process of setting it up, that the browser extension does not support Flatpak based browsers: "Please note that in general Flatpak and Snap based browsers are not supported, Ubuntu's Firefox Snap being an exception." (https://github.com/keepassxreboot/keepassxc-browser/wiki/Troubleshooting-guide)
Some others on ProtonDB are reporting this. For me switching to an older version (7.0-6) worked fine.