This is the last of your concerns. Enemies are allowed to have multiple copies, because devs were too lazy to implement a proper PvE. Relax, once Arena is out and they figure how to break it - you’ll have your “fair enemy teams”, hehe.
See, the game revolves around 3 dragon types. Sometimes a 4th broken dragon appears in the quests, and this isn’t the worst thing to happen, but generally the UI gives you 3 dragons, and that’s what you have to deal with. Whether it’s the code limitation or laziness, but the central dragon is usually alone, with few scenarios of double minibosses(more often than not - they are weaker than normal dragons). Which leaves normal waves with TWO, only TWO types of dragons, and there are some compositions, where even normal dragons are of the same variety(2x Muck\Tumble, 2xValiant Scarbearer, 2xFanghook etc), but, to make it competitive - there have to be up to 5 dragons, so they have to copy.
Yes, sometimes it breaks the game. Very rare occasions of 4 Skrillcrushers, Obsurdians, Trickies or even Shifties. Also 4 Torches, because they STILL haven’t fixed(at least not entirely) the enemy upper row dragon energy bug. But these cases are rare and devs couldn’t give less zit about them. Or about enemies appearing in random locations and numbers. One game you can have 2 Skrillcrushers bottom row with 3 Fireshrikes top row and that’s sort of doable if you know how to combat, another game you get 2 Fireshrikes bottom row and 3 Skrillcrushers top row, one of them energy-broken. This is, unless you are SEVERELY lucky - is a suicide, because the game just raw-docks you. Either you have Shifty+Toothless or you bend over.
Anyhoo, what exactly would you want to stack, huh? Five Trickies? Good luck with that. Sure, you’ll be an itch to kill, but you won’t kill anything either, plus over 60% of your efficiency will overwritten. Five Knock-Rockets? Also a funny experiment, but, from my experience with enemy 5 Chestnuts - not failproof.
In fact, more often than not - enemy stacking is actually what limits them. And if you pay a few hundred bucks and land some prayers to RNGesus on a Thunderdrum draft event - you might even get a Shifty, and that’s the first step to fighting back against these broken comps.
But there’s actually an easier solution that works for campaign - 100 rune revival, or a pacifier, in other words. Legal cheating. Definitely a cheaper way to progress through something broken, assuming you are otherwise prepared.