Sounds like I underestimated PoS, it's just that I never tested it - looks too boring to try - and I prefer not using potions when playing something other than a potion race or Chemist. Also CB is one of those items I try to avoid because it's too good, makes everything too easy.
Since I believed PoS is reliant on using close to all mana potion, up to 2 schadenfreudes and CB I wrote it off as a gimmick. Sure it's nice killing things that brainlessly, but what wouldn't work with such a crazy amount of refill?
However as you said it works with very little amount of refills too, so it's worthy of being called strong.
When I said hitting a monster into monster is only useful against bosses, I meant that 1 of the targets should be a boss, not necessarily both. When neither of them is a boss you could kill them resource-free 1 by 1 with wall hits if you incorporate a level catapult for the harder kill. This was only mentioned on the assumption that PoS wouldn't work well on harder Vicious runs, since it does, how you use KB should be decided by what you are looking for: a fun game or easy gold.
On the topic of 'Acid Rats' to weaponize indirect KB corrosion damage better all you need to do is corroding more than one monsters at the same time. This way you create multiple 'corrosion bombs' for the same amounts of tiles. You could easily get to the bossfight with having some low level, high health meatmen almost fully corroded. Each Pisorf cast could deal over 100 damage, and if you set the corrosion on your fodders at around ~99% of their hp you can use them twice for maximum value. With high enough max mana you could kill anything without even refills, there's just no need for it.
Applying corrosion directly on your bosses takes way less time and effort.