Not true. Any temperament will work, but some have different
compromises than 12TET. Playing an instrument tuned to 1/4 comma
meantone centered around C in C# may be a rather dissonant experience,
but it can be done and is actually correct for some periods of
music--and might be useful for the strangeness it imparts to new pieces.
But that is an extreme example, as the various well-temperaments can
work in all keys as well, but emphasize some over others. 12TET simply
emphasizes none and some would argue that it hurts them all equally
because of that. It is _A_ solution, but by no means the only one which
is workable or musically acceptable........................