Yeah it was just a handwaving figure.
The point is that in reality, no matter how ideal you want to pencil it out on paper, things you don't plan happen. In those situations where you can squeeze out just enough for even one more heal, you can save the day.
This isn't something you balance an ability around and it's not something you strategize a fight around. It's just one of those "I am glad I can make mana out of thin air" moments that abilities like TC & Solace can provide since they're absolutely granular.
Math is awesome and you need to have some rough numerical basis to balance an ability around for sure, but all the math in the world doesn't answer the unpredictable question of how many player errors will occur per fight.
I'm assuming this gets much better as haste levels get higher.
Solace could probably use one of those Runic Corruption gimmicks where its return scales inversely with Haste to make it always provide basically the same return on cast time investment. I don't ~think~ it has that already, but in a forward-planning sense it would probably help boost the ability a bit right now and stave off future nerfs.