By "legitimate" I mean artists who create original, creative works and contribute to the cultural and artistic ecosystem, as opposed to anonymous, mass-generated content that seems designed primarily to exploit platform algorithms

They release records and play shows.

I hear what you are saying but that's kind of an established-music-industry centric view. There are all kinds of musicians, not just "recording artists" in the 20th century industry mold.

There’s a rich diversity of musicians beyond the traditional "recording artist" mold. My concern is less about sticking to the established industry model and more about ensuring platforms support creators whose work reflects genuine artistic effort and expression

Do those not also get released as records and do those artists not also do live shows?

I know of at least one record label that specialises in releasing game music and I’ve seen Amon Tobin (producer who make the soundtrack for a Splinter Cell game, amongst other things) live.

Some composers do that, but most do not.

Movie and game composers are literally work for hire. It's their employers who may or may not release a record related to that employer's work that may or may not credit the people involved.

Even the extremely successful and popular composers are not necessarily releasing records or doing live shows. Even John Williams is primarily a conductor and a classical composer who didn't really start "touring" until 2002 or so. Same for Hans Zimmer. He doesn't release "records". Studios hiring him release movie soundtracks for which he was specifically hired. Etc.

According to your definition of "legitimate artists" these artists are not legitimate.

there's probably a difference between doing maybe a handful of live shows spontaneously, and having a career that's filled with live shows and tours. having a "record" (a whatever physical release) is kind of irrelevant cause anyone can put anything on anything, live shows and tours are more complicated and some people just don't do it, and it's a yet more bizarre way to measure "legitimacy" cause again, so much music and so many artists just don't do that.