For me, the major problem with historically informed performances is that,
while they might play on period instruments, keep the size of the ensemble
historically correct, use the original metronome markings, etc...they
can't replicate playing techniques that are no longer taught...things like
the use of rubato within a phrase without losing the overall beat,
measured portamento, etc. I wonder what Beethoven would have thought of
the Nikisch recording of the 5th or d'Albert's broadcast of the Emperor.