In general speed is very important. Even the hp buff, maybe directly for longsword of 2hs, can make infantry more appealing.
However, some people like that infantry line maintain its role after feudal (eagle/trash counter). But I would like to see some more use of infantry.
+1 melee armor to the Swordsmen line starting from Long Swordsman in combination with Supplies is enough to make Swordsmen cost effective vs. the Knight line when Swordsmen outnumber Knights by 2:1. Mix in Arson for base destruction to force fights against the mobile Knights, and this will give infantry a non-niche place in Castle and early Imperial Age. Infantry can keep their soft weakness to archers, just like archers can keep their soft weakness to knights.
That, or give Swordsmen bonus damage vs. cavalry.
That is the Spearmen job.
True, but then Teuton, Malian and Goth Longswords would be brutal to counter.
Infantry already does well againts Knights, Pikemen are Infantry. Againts Archers… well, Infantry does need a counter.