I feel like 5 minute blitz forces me to think on my feet and see things quickly. It might end up being self limiting but I can see that my blunder rate has been declining. I get relatively immediate feedback which has to be good for something ;) As a rank beginner that's something. I enjoy it and I don't need a large open time slot to play a game.

I should play longer games I guess. I do much better on puzzles when I have time to think through the move. Donno if the lichess ratings are comparable but my puzzle ratings are much higher than my blitz ratings...

I think that's a bit limiting as a minimum, 10+2 sounds more reasonable for a new player's introduction to a faster pace chess where they still have an opportunity to calculate lines; 15+* is certainly a great time control to play though.