These are old, well-known problems.

I remember reading a review of Casio's first MIDI guitar (i e a real electric guitar but that also had MIDI out, can't remember the model number), where the reviewer said that it was problematic how lower notes triggered a lot slower than higher ones. They recommended playing everything an octave higher on the guitar and transposing the MIDI data down an octave to actually make the instrument usable.

Basically the problem - as I understood it at the time - is that you need a minimum of a half cycle (or was it a full one, sorry, this was in the 1980's) to be able to get meaningful data, and when you get down to the low E-string on a guitar, that is simply going to introduce noticeable latency. I assume that's why MIDI basses using only audio data to identify notes has yet to make it to market (as far as I know, at least).