Teach me, expert players of Armored Princess

[impy]

You see, you admit yourself your black dragons sometimes have hard time and therefore are not that useful. and it will not get any better as the game progresses. Maybe it is time to replace them. For example: take advantage of paladin's circle resurrection. Get archer unit which will stand right next to paladins and will get resurrected along with them at the end of the battle. Or get summoning units - royal griffins, demonologists, demons, dryads..that way you get expendable meatshield.
You will have to replace all 5th level units before end game battles anyway.

I do not follow your skills selection. Yes, even on impossible no loss game the middle game tends to be not-that-difficult, but still..
Mage character should specialize from the beginning.
1) Devastator : high intelect and mana, casting pretty much only damaging spells - geyser, death star, fire rain etc. This character ignores light magic, transmute, order magic and goes quickly after chaos 3, higher magic, concentration, destruction etc, hero equipment boosts primarily int/mana, mind tree also focuses on int boosters first.
2) Supporter :buffing/debuffing armies - summoning, battle cry, slow, fear etc. you name it. This character goes after distorsion, order, transmute, higher magic,summoning, while chaos, concentration, mana/int boosters are delayed. Mind tree - prayer, persuation etc.

Idea behind specialization is to excel in certain field.. As you can see from your chosen skills, you have bit of both; neither strong spellcaster or strong supporter. Your game maybe doable as it is, but if you are looking for perfection

But, I am suprised with your might tree skills.
Mage,as we know, does not generate as much rage as warrior, and apart from very rare dragon dive only casts mana acc., lightning ball + treasure. Now how many levels of pet dragon do you need to max out these 3 skills? 30 max. Is there therefore a need to boost dragon experience? No. Remember, you cannot use pet dragon in boss battles anyway. I personally go for rage around 50 only with mage, just enough to cast maxed lightning ball and have some decent calm rage. So Rage control 1, training 1 - but only as prerequisite for Anger 1-2. With rest of the runes you can either go after frenzy or boost your defence.

P.S. you do not mention to have concentration skill. I'm sure you have it. There is a reason why it is all the way at bottom of magic tree - it is one of the best