No offense meant, but how is that abuse?  Consider: time stops in a battle, for good and worse.  When you return to the strategic map, any damage you've suffered in tactical combat will (from the standpoint of the strategic map) instantaneously appear there, and so will any healing you've done.  They're just flip sides of each other, the way I see it.  And it isn't abuse to hold off an opponent, stronger or weaker, to let a regen spell knit bone and flesh, anymore than it would be to take a healing potion.  Unless I'm missing something else in your argument.

Now Regeneration enchantment is OP, because it really gives you full health all the time between battles for as low as 15 mana and 1 mana per turn. Also it causes you to spend time on skipping many turns in tactical battle. It is boring like kiting monsters. Imho it should be fixed.

Correct.

seanw3 has the right of it. The problem is that regen is not overpowered it is a problem of tactical regen vs. strategic regen. There should be more regeneration per season and less for tactical battle. Another alternative to this is that regeneration is only a strategic spell so that you heal quickly on the strategic map, but not in the tactical battles (although I don't think people will like this option very much).

I can agree to Strategic should do more.  I can also agree to Tactical needing a fairness buff.  Explanation: Trolls regen 4 hp a round tactical.  My suggestion is the base should get upped to 4 plus extra per shard (Same as Trolls get nothing more).  This spell is only for the very early to early game as it is and super weak.  A small kind of bump, it might be somewhat useful for midgame.  While it may not stop you from getting destroyed late game. 

Re: Death.  Oh please.  While drain life is not per turn, you get to damage them and heal yourself.  Considering how weak the per turn is.  Yeah.  Death Magic still king. Or curse/mass curse and kill them since their defence went to zero for 3 whole turns.