Nice to read about your progression
I assume you are not medium weight ?
As, when you start the very first few times you are typically better off being powered like you are used to (which is WAY too much for hydrofoiling when you can do it).
But in 15-19 knots I would use a 9m2 on my waveboard (not foilboard), and a 5 or 7m2 on my hydrofoil (7 in 15 knots and 5 in 19 knots).
Regarding the "slower turning", yes, it is good when learning
Later, you will appreciate really fast turning kites though, as you can handle and loop these whenever you want, when doing carves or jibes.
Or, let me phrase it opposite: There are no downsides with fast turning kites when you got the hang of it, and the advantage is you wont drop the kite as easy anymore, because if you do, you are in for a swim yes
Just noticed the sizes you choose, when you had learned to foil some - as these are normally only used by heavier riders and racers