In the 90s I played with a group that had a horn section who were mostly Disney players. A trumpet player wrote the charts and 90% of the stuff was in Bb or Eb. He was a working pro & had a good reputation as a player. They did dictate changing keys. Singers could get agitated. I just played guitar so I went with whatever key was put in front of me.As a horn player, I can confidently say that horn players don’t give a **** and can play in any key, and don’t try to dictate anything. I played on reggae/ska/dub bands for years and everything was in ‘guitar keys’ and no horn players cared. They aren’t scared by flats or sharps.
On the other side, I played outside of that situation at times with a couple of the sax players (one had played in Liberace's band & the other was a doctor who put himself through school playing) and neither of them winced at any key or arrangement.