Since we go grocery shopping all the time on bikes (no car for us), I need to have pannier size and type to be flexible for multiple purposes. Trunk bag would not suit my needs. Too limited.

I also have taken some art courses where I stashed several tubes of paint, brushes, water container, palette paper, etc. and lugged them along on bike. Along with drawing board, sometimes whole large rolls of paper, etc. strapped on top of rack. Again trunk bag doesn't help.

Work commuting, I need to fold my clothes properly without wrinkling too much.

Going to different bike stores to try to find a rack that is long enough and high enough does help. I take time to find new pannier shapes so that I never have problems with kickback (yes, it is what you described).

I've been cycling for over 18 years. Have gone through 3 different types of panniers 'cause I really use them well all the time.