I agree that I need some quicker attacks to clean up smaller groups of enemies. I was thinking to add a weak non-spell gun to the plane, but haven't thought through whether it would be better to have a quicker spell instead (or maybe have the power of glyphs scale with size in some way). Don't know if you tried, but currently it's possible to cast glyphs faster by drawing it smaller (there are controls for adjusting the size of the guide, though when it gets too small it's easier to not use the guide since it's easier to adjust for mistakes).
What did you try for the time slow? In the tutorial I forgot to mention that you need to hold the input, so maybe that was the issue. Dodging is currently kind of hard without time slow, other than very coarse dodging to avoid most of the shots. Releasing your drifts when you're about to be hit can help by making the enemies overshoot.
The other points are fairly straightforward so I don't have much to comment on them. Thanks for the detailed feedback!