I could not agree more with you. While every person should be encouraged to play music or experiment with sounds and timbres for enjoyment or personal enrichment, and modular makes this so fun, there is a reason why the best piano players like to play Scriabin or Prokofiev, for example, pursuing a synergy of technique and expression.
Also a reason why composers will write music for specific performers, like Ligeti did for Gawriloff and Aimard.
As you alluded to, a drummer will not play bass guitar like a guitar player either. Usually they play it better.
Let’s not underrate talent either. That’s how you get “fugues” in electronic music that are not much like the real thing, not compositionally rule-based at all, and music lacking in musical development. Not to mention singers who can’t actually sing, and would have never ever gotten a record deal in the 60s without a successful performing career first. There is a lot artists today can learn from the past; that goes hand in hand with appreciating the sound worlds of the past, as everyone here does to an alarming degree!
The entire period performance movement shows how instrument construction affects playing, and started when Harnoncourt and Leonhardt, among others, bothered to try playing the old things and thought about rhetoric, “music as speech” in cantatas. Now there is a cottage industry of harpsichord replication and restoration of Ruckers, Vater, Hemsch, etc, Walter fortepianos, and fully recreated instruments like violoncello da spalla.
It’s not always dogmatic either, you have natural brass mixed with modern strings, even romantic pianists playing on Erards and Bechsteins again, but not on every piece, because the expression changes with the idiomatic playing of an older style instrument. And you have reactionary conductors who like their Bruckner without any diet regimen, and players like Víkingur Ólafsson who play Bach and romantic transcriptions of his organ works on a modern piano - that’s cool too.
In any case, the best modular performers really do tend to master their instruments, as antiphon pointed out.