>The whole point of Bach’s Well-Tempered Clavier music is that tunes transposed to different keys sounded different, so you needed to compose the music specifically for each key.
that sounds wrong. tranposing a piece into the instrument's natural temperament will make it sound better. TWC doesn't do that, you play a piece of any key without needing to transpose anything, because the piano is equally-tempered and has no natural temperament (without going into how "well temperament" differs from "equal temperament").
for instruments whose tuning can be changed with technique, like string instruments (even fretted ones), wind, reed and brass instruments you can revert to playing a pure temperament in order to make certain harmonies sound "better", which is what we sometimes did - for example, by getting the minor third instruments to play slightly flatter - in a symph band.
> WTC doesn't do that, you play a piece of any key without needing to transpose anything, because the piano is equally-tempered and has no natural temperament
The Well-Tempered Clavier was not written for an equal-tempered piano.
Playing it on a modern piano gives you a different sound than you’d get on a harpsichord or clavichord or whatever tuned as Bach would tune them (from what I understand it’s not entirely clear what this tuning should be though).
(Caveat: I’m not remotely an authority on this subject, but just some guy on the internet; consult your local musicologist / early music expert for better advice.)
that sounds wrong. tranposing a piece into the instrument's natural temperament will make it sound better. TWC doesn't do that, you play a piece of any key without needing to transpose anything, because the piano is equally-tempered and has no natural temperament (without going into how "well temperament" differs from "equal temperament").
for instruments whose tuning can be changed with technique, like string instruments (even fretted ones), wind, reed and brass instruments you can revert to playing a pure temperament in order to make certain harmonies sound "better", which is what we sometimes did - for example, by getting the minor third instruments to play slightly flatter - in a symph band.