side question. Are knights given an actual tanking role in your guild, or are they considered a 2nd-class citizen, merely good enough to grabs add / pop a deflection?
Actually they don't as far as I am aware (but it can only be proved through testing). My limited testing with resplendent glory and hold the line (tank discs) and some rough wags at the heals landing numbers strongly suggests to me they do not add together. If on diff slots then yes they can both be on the same tank at the same time, but the higher one is the only one that takes hold.
Those don't stack because they are the same slot. Try looking at a spell parser. Example Given: Lets say a Paladin hits their 2.0 (40%), First spire (30%), and AOTI (74%). Heals are increased by 144%, not by 74%.