Yeah the problem is more like the fact, that most players won't abuse it. Also in teamfights it's kinda worthless unless you get a rare of a kind long poke fight.
I would change the cast on teammate effect.
Casting on teammate would give a healing over time effect, that heals up to 5 seconds charge ticking every 0,5 seconds. So you could heal better on the move. Cannot be stacked with itself. If you got those basic attack buffer stuff, then you would sacrifice one when you use on teammate directly for increasing the heal over time for the full 10 seconds period.
Casting on ground would work as it is now. It's great for early, game, and for special cases still. But for teamfights, and fast moving fights the cast on teammate would be a bit stronger. Casting on ground also remains as instant heal which can be stacked 3 times. So it would still worth using it, if you got the time.