My experience has been that EAC is a problem at the top of the list, and there's an enormous middle of the list where things just work, and a very long tail of older games which don't really work at all. (Once everything became unity, the problem got easier, I think...)
There's a (very) long tail of games that surely receive less attention (by the Wine/Proton teams).
Additionally, a large part of the top ones has a native port, which smaller production companies/indie devs typically can't afford.
On the other hand, smaller games could be simpler to "not emulate" (:^)) due to them being simpler.
> they have committed to bringing all Steam titles to the Steam Deck running SteamOS
This is unrealistic.