I think that people, if trained by a band putting resources and often considerable time into them, would tend to play in the clef for their particular instrument that is used in a brass band. There is nothing wrong with this because the players play for the band first and themselves later. Any decent players will naturally learn all clefs when and if required. There could be said to be a special case with the trombone because it uses so many clefs, but as I said, any decent player will learn them all eventually. People learning at school without reference to a brass band, however, will normally learn in the clef as used in orchestras. I know of a county music service local to me that now buys (and supplies) trumpets instead of cornets. Because they're cheaper!!!?
Personally, I learnt bass clef trombone from teaching someone else it. I now can play in either on trombone or euphonium. Didn't prevent a few mistakes though (i.e. play that F..... I mean G etc.).
p.s. Geraint Griffifths (faireys BT player) as I recall, doesn't read in bass clef, but transposes everything! End of story, He's pretty good, eh?
p.p.s. aren't tenor trombones pitched in B flat. Why not C?
As for perfect pitch, it must be a curse. Relative pitch is much more useful.
I'll get off my high horse now in a cold sweat (my first post finished- fingers crossed)