Appoggiatura lasts way too long on playback

This would be an acciaccatura not an appoggiatora. The former is not only shorter but would also play before the count of the main note. An appoggiatura is always played right on the main note's count.

Marc, I also struggle with this execution of appoggiaturas. You refer to a quite strict look at this but there is indeed much dispute on this point. Some say that up to C.P.E. Bach, this is the correct manner, but later composers tended to write the intended values in grace notes, to have expanded means of expression. Some even say that it was always up to interpretation, and it was never that strict. I am not to decide what is right here, but don't you think a writer today should have the freedom to use the notation they prefer and get the expected results? If they want to write and playback in mannered baroque style, ok. But if they want to write e.g. all these quick hammer-ons and pull-ofs for a contemporary guitar, they will usually want to note them as grace notes, and to playback them in the correct values. This also gives the player a guidance in that the main note denotes a chord note of a certain voicing, and the grace note denotes the playing around that chord note. Of course they could write all the figures in regular notation, e.g. a semiquaver and double-dotted crotchet. But that is not only tedious writing but also uneasy to read, in particular in multi-voice scores. So I would indeed see some need for a flexible handling of grace notes. I also guess for those who know how to do, like you are, it would be easy to implement e.g. in the properties how an appoggiatura shall be played.