The problem is they don't "let the developers do the work themselves"
If only the platform was open enough that developers had real access, Apple might get away with like you say not providing first party support for gaming.
I mean it more as a counterpoint to what Valve is doing: games are automatically opted-in to working with Proton and pass through a Valve-operated certification program. Because developers aren't part of that loop, you see occasional cases where games issue updates that break compatibility, with users blaming developers based on an outdated, Valve-provided certification.
If only the platform was open enough that developers had real access, Apple might get away with like you say not providing first party support for gaming.