IMO the most important nerf to inf in history was the forcefield "fix" that almost killed kite/heather/board shields and severely gimped all others.
Also, armor nerfs, including the upkeep patch (although it is true it hurt cav a lot more). Pike/long spear nerfs, 2h lolstab nerf, all the knockdown weapons that lost it... That's about it for the "global" ones.
However, every single (used) melee weapon got nerfed at some point. Unlike cav and ranged that usually are treated as more homogenous groups, melee is nerfed/buffed one or a few weapons at a time. The more global changes are usually done on cav/ranged, which means buffs too.
I think it is justified, as the melee mechanics are much more sensitive to change than ranged and cav ones. Also, we want to keep the melee system nearly intact because it is truly great (at least, it was great before the neverending block battles and the focus on footwork that ensued), unlike cav and ranged mechanics that are less complex to say the least (I'm not saying playing those classes is less complex though).