KCH struggled vs more than 1 rifle squad, struggled vs Vet 3 rifle squads and allied cqb elite infantry, were hard countered by vehicles, and lost a good chunk of HP to mines. They also spoonfed vet to rifle squads if you could outnumber him in a fight. They were not OP, period.
But even if they were OP, that would be an issue with that particular unit and not the entire system.
Target-tables do exist which generally plays into armour types, but they shouldn't be the go-to or you have a ton of things that need to be memorized regarding how unit X performs against unit Y. It also could lead into the actual unit not being fixed to perform its function, but band-aided solely against that one unit.
You're overstating the complexity. There were 4 units with soldier armor, 2 with elite armor, 3 units with their own special armor, and the rest with standard. Only a handful of things are important to know such as use flamethrowers vs elite/soldier, snipers vs elite, SMGs vs soldier/airborne, and elite/soldier very effective vs BAR upgrade. A lot of variances were for fine tuning the balance and weren't pertinent to remember.