Healing Direction - is the current design balanced?

[Daenerys_Sedai]

Also means you then have to overheal with more MP or let the HP bar fall lower instead of shooting a low MP less HP healing spell.

This is the best counterargument, I think, to non-tiered heals.
Of course, we don't know what MP bar progression and costs will look like yet, so the "costs" of "overhealing" may be negligible.