On the last point, most of that latency is from the touchscreen response, the audio system is capable of single-digits latency.

Things may have gotten much worse recently as I distinctly remember the iPhone around the 4s-6s era having <30ms latency which was a huge advantage over Android.

The Apple Pencil can also go under 10ms latency when drawing, there must be a way of taking advantage of that for music apps?