Honestly Hedgie, making minions unable to attack Citadel doesn't make much sense. After all, if they can tear down citadel the way they do is because they've been able to easily destroy every single defensive turret before it. Then, why not making them unable to attack turrets/forts too? It wouldn't make much sense either.
The other fix you suggest looks overly complicated.
If i'm not wrong the heal % of priests doesn't escalate that well, it goes from 10% of Monks to 15% of Bishops, so upgrading priests idols ain't that great, it's the HP stacking that makes the difference. IMHO opinion it's only a problem early game where choosing Blood of the Fallen over any other favor item makes a huge difference in monks heal due to their % based nature.
My main gripe with minions is this:
-They're supposed to add some RTS strategic depth and variety to the game, but: in good RTSs you have to take care of your units because they cost precious resources. But in Demigod you can mindlessly throw them at enemy towers/whatnot cos they respawn themselves OR at a very low mana cost, with a very litle cooldown time. In addition to this, enemy demigods gain nothing by killing them, no xp, no gold, no nothing. So this turns demigod into a bad spamfest RTS.
You can fill your inventory with minion enhancing items without caring much for your mana pool or own hp, since enemy can't reach you behind your minion wall. So, i'd really like to see an increase in idols summoning cooldown (let's say, being conservative, 45secs), and maybe a lil increase in mana cost.
This way, going for those monks healing that enemy demigod could make a difference, they'd have to wait a bit more to just respawn them, and you could concentrate on the demigod itself.
And of course lower the retardedly high hp that sieger archers/demolishers have, they're moderately gold cheap, have high ranged damage output, and yet they sometimes have higher HP than the summoning demigod itself (2 x 1575 hp siege demolisher = 3150 hp
).
Ah well, i'm a crybaby.