Nerf Knight's DR and add 15/30/60% Tenacity. This would at least give Knights a niche that isn't straight up worse than Brawler's while also nerfing how goddam insane stacked Garen/Darius w/ 2 Knight buff are in the early game.
It would give Knight comp late game relevancy outside of Kayle.
Overall suggested change:
Knight 2/4/6
+20/40/80 DR ==> +10/20/40 DR
- +15/30/60% Tenacity
I still think Brawlers would be straight up better, but at least Knights would do something now.
Can't make Tenacity too high though, otherwise one of Kayle's weaknesses w/ Shojin stack (CC) becomes too irrelevant.