Thanks for the reply. About balancing, yes it may make sense over time. You could do like Octopath and reduce healing power to 30% so boost is always useful for it, but with the current enemy power it is easy to lose 70-80% of HP in one non-Defended attack. This means you often need an emergency heal and therefore being able to do what without boost is useful (but if you make enemies attack a little more often but with weaker moves, this issue may disappear).
Otherwise you can go the I Am Setsuna way, using boost to give a qualitative extra side effect, such as continuous regen or status healing. This way boost is useful for the impact is not quantitative on healing. Note that I Am Setsuna actually uses “Momentum”, which is what you call Overtime; so you could use Overtime for those extra qualitative effects instead. The main difference I noticed in that I Am Setsuna’s overtime is manually triggered).
Speaking of which, I Am Setsuna’s Momentum is limited to 3 full spheres, to prevent stacking and encourage player to regularly use them. Again, the difference is that your Overtime is auto-consumed, so a small number may be too limiting in case player consumes a little inadvertently.
I don’t have the detail for focus lost bug, but trying to play the entire game with keyboard only, or gamepad only, is a good way to verify that focus is stable. You can even click outside buttons and stuff to make sure you still don’t lose focus (btw a Unity setting can prevent focus lost on click outside, but I didn’t test that so maybe it was already enabled).
Wow, you remember my post on Spirit Link! Thanks, we’ll do our best!