In the old days, mana was the hard limiter for druid healing effectiveness. Looks like they’re getting back to it a little.
Also, I would guess that the vast majority of druid healers don’t even know where Innervate is on their bars.
Also, you can choose talents that help. In the last row, for example, there’s a talent that increases healing effectiveness quite a lot without requiring more mana use. Casting a second rejuvenation on someone, on the other hand, does require mana. Yeah, there are trade-offs, but you do what you need to do.