The issue isnt that it's a level 70 ability it's the ability itself. There are instances in dungeons where cure 3 is better then either medica in dungeons, the only one I can think of right now is the hraesvelgr fight where the party is often stacked and the blue beams drop for a lot of damage. Other then that there are other times when the party stacks to take damage, cure 3 isnt used often but it has uses even in dungeons that arent overhealed. I'm not asking for something op because it's a 70 ability, I'm saying that even though I think the changes I would like are balanced, some would say it's op and in comparison to similar spells (Tetragrammaton and thin air), it's not actually op
Honestly the change I'm proposing wouldn't make it much different in raid battles since it has a longer cool down before you can use it again and the fact that the confession is on when you need it isn't much different then casting medica 2-3 times and using PI right after because your still using PI during that heavy aoe part. The only difference is you aren't forced to use it within 10 seconds and the max potency wouldn't be as high. Other then that it's basically the same in raids so it wouldn't make whm op in raids any more then it already is.
I can't really say much about the comparison so assize except it is pretty similar to assize even now. The only difference is potency and the fact that you can have more stacks. But you could just as easily do a few medica 1 or 2s and finish off with an assize to top off for a similar end result during heavy aoe parts. Basically wether it's changed or not it's still pretty similar to assize either way accept that PI is more limited
The 60 seconds could be dropped to as low as 30 as long as you can refresh it whenever you want but the strategy and balance of using it is based more around the cool down being so long. You have it whenever you need it but when you use it make sure you won't need it anytime soon. That seems like it works for everyone.
I don't doubt that it shines in raids currently but even most raiders don't do only that, it's only an improvement to make it useful outside there too. Again not everyone does raids and it should still be useful for everyone, especially because that's not a crazy request, it's absolutely doable