Hello fellow KB player
As you stated `exploit` isn`t really bug or error in game mechanic, it`s only way to play battle for 1hour(or more) which isn`t interesting.
And it`s against AI so you can`t be all tough
It`s only way to replanish mana/rage between battles. So question is why would you spend so much time on battle that is already over, 2-3 rounds bonus to get mana/rage and resurrect units OK, but anything else is pure waste of time. And later in game there are some sick enemy combinations so your exploit wont work very well against dragons,demons(archdemon, demoness), almost all elves(fairies,dryads,unicorns)...
I played original King`s Bounty some 2 years ago , but i`ll try to give you some useful information.
As you stated in conditions : mage hero, intellect,mana,lds, lina rage spirit with maxed charges. First about this you`ll need to be at least 15lvl (almost half game played), in dwarf lands and enough battles to lvlup Lina for that skill. So you`ll already play some time without this `exploit`. I personally never managed to kite there without fighting couple battles in underground pass to dwarf lands(so no low lvl lina spirit).
I tihnk chargers are landed random, so no sure way to stop enemy form using them. Also why barbarians ? As i remember they aren`t controllable (or at least in AP), so no way to stop them form killing last enemy unit.
And in the end, no AP dont have this exploit, because there are rage spirits, only pet dragon and his skills are different (which is shame, i miss rage spirits
My advice is try CW (Crossworlds), just skip AP and get some of mods red sands is among best by my opinion. Many things are changed in AP/CW so some of things you use in KB-tL wont work in second game. Have fun with this great game