Disagreeing with you and a dude with a degree from the University of Bristol from the UK with a degree in philosophy and psychology on how bad Knighton was does not a putz make.
https://www.linkedin.com/in/john-breitenbach-975755113
Other teams pit, bal, houston, have dedicated NT that play limited snaps and they make rosters. Knighton was just bad according to (literally) every Cooley Film breakdown from 2015.
Using Knighton, a bust who can't make a roster in his prime years, is not a strong argument either way on the importance of the NT position.