The biggest issue I have with most car and airline seats is the back curvature is completely wrong for my height. So even in a section or vehicle with ample leg room, there's a hump on the top of the seatback that does terrible things to my shoulders and neck.

Exactly my problem. I simply cannot use the seat back properly at all. My head cannot lean on the head rest, my back does not align with the seat. I just sit with all the grace of sitting on a stool.

I don't usually face a big problem with legroom. My legs are cramped but they fit. The bigger problem is relaxing and sleeping. I can't read on planes for longer than 10-15 minutes (I have to raise my kindle to my chest level in front of me, if I don't want to bend my neck), and the seat backs are just uncomfortable. I can't lean, can't sleep because my head rises above the headrest. Add the general lack of space in the standard economy seat and it's very uncomfortable for me.

Longer legs than you? I'm 6'1 and my knees already touch the back of the seat in front of me on regular airlines.