Xers have the most influence in Culture.
we should probably define who we mean-ish. at least broad strokes.
So, Brady's an early millennial. There's football. No but seriously, the currently passing tranche of athletic talent (currently going away) is the Brady, earliest-millennial era. You might even argue for Brady, the old guy, as a late Gen Xer. But almost all athletes on the field/court are currently Mill/Z. But they only influence culture when, like Kaepernick, they step outside their role as athlete. Kap actually had an ENORMOUS cultural influence, more than Brady ever will, because of what he said/did having to do with the Nat. Anthem in intersection with the BLM movement.
In music you might be right. Lin Manuel Miranda was born in 80, that's X. But I think - THINK - he's offset a bit from those who are his most ardent fans (although it's hard to choose... he appeals to 70 year olds too. And with hip hop at that. Not bad.) Also the royalty of hip-hop, the dominant culture in music, is of that same rough vintage. Eminem, JayZ, Beyonce. etc. That is mainly because Hip-Hop is so new itself that its founders are still around. Rock is pretty much the junior (smaller) partner now in music and is even more loaded down with older icons. But again, that's through my eyes. The landscape is fragmented now, and I am used to a culture of albums. Now it's a culture of surfing and exploring. By the way, I recommend this Mongolian throat-singing band called The Hu. I **** you not.
So culturally, I can only look through old man eyes and describe the culture as celebrated by other aged institutions. I'm TV heavy compared to Xers and younger, and my online habits are like you'd have in 1999 or so, with the addition of facebook b/c old people LUVS us some facebook.
When I browse around quasi-randomly, or take in a kinetoscope for the younger crowd, featuring popular crooners and hoofers, I think I might be missing the proportionate influence of the younger set - they're not the kings and queens anymore, but the sheer numbers are younger.
If we mean computer icons, the hardware is boomer-descended, but necessarily what we have at a given moment is built by folks younger than X. In fact, Apple commemorated the last generation X engineer with its iphone X. It's all millennials and Zs now. Just kidding. But the guts of our culture is built by the young. The broadening behinds of the boomers are largely (heh) fading out and the rest of you are starting to see the sun that you've been climbing toward, if you actually had a "stuck" company job.
This one is kind of mind-blowing... politics is so ruled by older people, that Obama (a year older than me) STILL represents that breath of fresh air of a youthful president. (I mean, Bush was when he started, sort of.) But think about it. We STILL have not only never had a woman president, we have not even passed the baton to Gen X (Obama was trailing-edge baby boom.)
Kamala (b. 1964) would still have baby boom status by some reckonings.
But who are you thinking of when you say Gen X rules culture? You might be right via music, see above.