Well...ok, here goes, you were Crewing, which means you were trimming the main going upwind and the kite going downwind, right?
Did you edit out all the 1000 times you looked up at the main going upwind and leading edge of the kite going down?
I usually tell my crew, "If I look at you and your eyes are not on that kite luff, I'm going to punch you in the head! DO NOT take your eyes off that kite luff!"
(any wonder I can't get crew?)
Maybe that's why your kite luff was too tight? At least it didn't collapse, which is even slower...
Upwind in steady breeze I never look at the sail and trim according to how much the
windward hull flies above of the water (ideally just above).
Its much more useful to look upwind at the gusts then to look at the sail anyway.
I want to keep the mainsheet as tight as possible to keep the sail flat and fast.
But if I pull it tight and the hull lifts too high I put on as much downhaul as needed to bring it down again.
(And if that isnt enough I will put on more diamond tension asap).
Downwind I do actually look at the luff of the kite but do a lot on feel as well, in lighter winds it is basically all I look at though.
Note to self: NEVER crew for Timbo!