We went from a champion with a toggle drain tank ult that gave you a ton of freedom in using it with the capacity for self destruction, to a glorified nuke that was based on whether or not they threw you someone who was safe to sucker punch before actually breaking out into the next team fight. Regardless of kit strength, there was room for improvement in the execution. I'm not trying to downplay the value of the current heal here, but you absolutely can't afford to not get that nuke off as Swain, and more often then not it means tapping out of the legacy part of his kit really early.
Ult wise, this is a nerf to his early kill potential against solo champs and longer time in the drain tank fantasy (even with full minions it's about 2 to 2.5 seconds extra before you're at the damage peak, which is about a fifth of the max duration), for a significantly shorter wind up in best case scenario teamfights, but with a higher opportunity cost for cashing in on the nuke early. 5 man healing, especially with the extra added bulk, actually gives a much more compelling reason to stay ulted and fight normally first, whereas his current state often comes off as way too frail for it and forces you to have a trigger finger on the nuke part. All the while no longer penalizing you for the enemy team choosing inaction in between uses.
So I think the added bulk and the ult changes are justified. The Q changes... I'm not going to pretend that they aren't something I've been wanting, but that doesn't necessarily mean we should have them. Extra pushing power (as needed as it feels) and the ability to punish melee's harder with Q (though this ought to be gated somewhat by not wanting to push early, and the mana returns being isolated entirely behind catching your opponent) are a lot of volatile power. On paper there's room for this to work though, and I think this set up is a lot more engaging to use, even if some scaling down ends up being necessary.