Paikis is arguing over spherical cows in vacuum. Again.
1) All that "old IB potentially mitigates more damage with it's heal than the new one" works with one condition: There will be few to none incoming heals from the moment you take your big hit till the moment you pop IB. Which is the case... Once in a blue moon or what? Because in every other case, when the tank is expected to get hit hard, healers make sure he's as close to being topped off as it gets. HoTs, heal pre-casting, you name it. And in this case, most of that old IB will become overhealing and get wasted.
2) Old IB has near-zero synergy with shields. Stone skin, Adloqium/Succor - they work wonders on Warrior due to high HP pool and that healing bonus. New IB will work nicely with all that, old one just won't. Again, "if" we're using direct heal spamming only (another cow in vacuum) old one looks not as bad. Switch to real in-game situations and there you go - that "nerf" doesn't look so nerfy now.