Ahh yeah, if you were looking only at games with native support then you'd have found an extremely small pool. Even games with native Linux versions often run better with the Windows one using proton these days. The big holdout is anticheat, which developers can choose to manually disable Linux support for (which they're motivated to do since there's no way to get them running kernel-level like on Windows).

Fully agreed on warning people. It's weird to oversell something you want someone to be happy with, glazing over pitfalls that might turn out to be show stoppers just means there's a chance they'll have wasted their time. Even if they're willing to put up with the little issues in the end, you're setting them up for disappointment. It's better to go into a movie with low expectations and be surprised that it's half way decent vs going in expecting it to be a masterpiece right?

EDIT: On that note, I should add there's still a small handful of single player games that don't run well, as well as some others that require tweaks (manually setting the proton version and/or adding launch arguments) to play well. You should definitely check each game you care about out on protondb before making the switch, if you're considering it. The one I've had issues with was Forza 6 (I've since refunded it), which had occasional micro stutters that ruined the fun- it had just come out mind you so it may have since been fixed...