But comets do fine? Maybe you're just using them wrong :/
The Comet's okay, but it's got the AI damage of a Cromwell, which has the AI damage of a pintle-less Sherman using AP rounds. You get it for an advantage in the tank battle.
You get about T-34/85 performance out of it: it'll merrily clobber Ostheer T3 and the OKW P4, but is countered in turn by Panthers up.
Which'd be fine if it wasn't 185 MP behind a 50 FU side tech. You've got to throw down 235 FU for it, which is more than a Tiger.
It's a good unit, but it's not worth 185 FU, let alone 235.