To some extent the combat system of World of Tanks resembles the combat system of Dungeons & Dragons: A first random roll determines whether you get past the armor, then a second random roll determines the damage you do. However where the two systems differ a lot, is the power curve: How effective are weaker participants against stronger ones. In D&D 5th edition the power curve is relatively flat; even a weaker monster still has some chance to hit and damage a higher level hero. In World of Tanks the power curve is very steep; you end up facing tanks you can't possible damage, at least not while they are in a typical defensive position facing you.

The steep power curve has an especially strong effect on heavy tanks. If your enemies are two tiers lower than you, you could be an invincible god. Next match, in the same tank, against enemies two tiers higher than you, your armor might as well be made out of cardboard, and your gun becomes ineffective. There is no way to have a tank on which the armor is still effective against enemies two tiers higher. But you can play tank destroyers whose guns will still work reasonably well against higher tier opponents. That makes your performance a bit more consistent, and you suffer less from the inevitable bad match-ups.

One of the probably unintended consequences of the steep power curve is the effect on premium ammo. Some tanks have guns that are good enough with their regular AP or HE ammo to take on any comers; other tanks simply become worthless against higher tier opponents if they don't load premium ammo.

I must say that from a game design point of view, I much prefer the flatter power curve. Of course a weaker opponent should have less chance to hit, or deal less damage. But if you consider that for matchmaking you need to be the weaker opponent sometimes, the game remains more fun if you can at least still do something instead of ineffectively bouncing against too heavy armor. Right now I'm playing a lot of tank destroyers because of that.