At two well-known points in WTC I it seems quite probable that Bach
altered a melodic figure to avoid writing a top C#. I don't see how we
can understand such places in the musical text *without* thinking
about what Bach wanted or intended. For example: 'Bach wanted ideally
for contrapuntal or melodic reasons to write a scale going up to C#,
but his intention to write a work within the range C-c'' (for whatever
reason) was more important and led to him altering the treble line to
the existing form'.
We also could quite sensibly say 'if the top C# had been much more
common on keyboards then Bach would have written it'.
If you can't tell the difference between this talk of 'intentions' and
the supposition that Bach could have intended to become an aviator ...
well, the mind boggles. And that from someone who considers himself an
expert in Bach's performance intentions as deduced from close scrutiny
of surviving texts.
The 'aviator' line seems to be a crude attempt to discredit any
thoughts about composers' (possibly complex and conflicting)
intentions. About as useful as the old argument 'if Bach had had a
Steinway grand'... compared to which Leonhardt is a model of restraint
and nuanced argument.