Why did you replace SOTA and not Bond of Stone

Could have easily just shifted SOTA into a scaling bonus % of health a la Cinderhulk instead of flat for focus on late game instead of early, and for good measure make it easier to stack in lane. Now non-tanks aren't abusing it to become obnoxiously hard to kill despite their full investment into damage and Garen gets to have a keystone that he actually works with. And it would have been just in time for buffs, so everybody wins.

bond of stone is complete non-gameplay. There's nothing to play around, nothing to work towards or stack up; no, it's just extra damage reduction. You never appreciate the mastery, but if you're a tank support that isn't cancer Alistar you're still probably going to take it. Why is this the mastery that you kept? Especially with the introduction of Knight's Vow, and already existing items like Phantom Dancer, an ADC basically gets a whole bunch of defensive stats despite zero investment into it. Did we really need to make them pseudo-tanky despite Riot balancing them around being full 6-item glass cannons?