You can change the speed of the game all you want it wont change the numbers, You still have to spend twice the amount of gold to get the human equivalent of an orc's late game dks and twice the amount of ticks (game time).
You can repair your mage tower and make air yes, now how is that relevant? Cant an orc player do that too?
And again if you do that with an orc you have the exact same unit when it comes out except you have Coil which is the best nuke in the game because you can use it way more often and almost as soon as your dks come out (mages and dks spawn with 85 mana).
Oh and you also have the option to get whirlwind instead of d&d which is slightly weaker but faster to research if you research that you dont even have to rep your temple.
In some situations whirlwind actually is better than d&d if you use it on a gold mine it will stay way longer than d&d there thus preventing mining more efficiently. if the peons where pulled off the mine they will have to wait more before they can get in again oh and you can retreat your dk as soon as the whirlwind is casted.
Yes slowing the speed down will make targeting moving units easier and since slow / polymorph / heal are directly targeted spells it will make it easier for a human player to cast these and get more value out of them.
But the imbalances do not only rely on the impracticability of these mechanics, numbers just do not add up.
You simply do not get as much value out of your clicks even if you manage to perfectly use your spells.
Paladins will barely ever heal each other back to full life because heal is expensive and it will cost you a lot of actions to try healing them.
It takes 3 actions to select pick the heal and apply it will never get you the same value as 3 actions to select an ogre pick bloodlust and apply it.
Heal simply does not heal enough for it to be worth it.
Lets compare in terms of mana / value:
50 mana heal will really heal 8 hit points.
50 mana Bloodlust will increase your damages by 3 for a level 5 ogre, so instead of 4-8 damages he will do 12-24 damages if that ogre lands only 1 punch this is already more value than heal lol.
Even if you made bloodlust disappear after the first punch it would still be more worth it than heal from that perspective XD.
Exhorcism along with skeletons and flame shield must be one of the most situational spell there is. think about it you can use it only on 1 unit out of the 15 units orcs have if you have 1 orc opponent out of 2 it makes it even more awkward.