Maybe the Cromwell VI's gun is too small, but I know for sure that it works with the M4(105). Try it out for yourself.
The Panzer IIIs and PaK 38s could combat the T-34s effectively in 1941. The overrated piece of junk known as the T-34 needs to be taken down from its pedestal. Nothing in the German arsenal but FlaK 88s could penetrate the thick front armor of some of the KV tanks in the early war, though. Even the side and rear armor of the KV tank was very thick by 1941 standards.
That piece of junk just happened to be rolling through the streets of Berlin in 1945...just thought I'd mention that. Round about early June '45 I don't think the germans were even capable of doing that....
In fairness though, you are right...right up until the mud and snow came. Then the germans had to lay down a lumber yard just to keep the tank's belly out of the mud, and a broom to brush the mice out of the wiring. I don't agree with the idea that T34's were impenetrable, they were, but they were designed to work in crap conditions, driven and fought in by kulaks, and deployed in mass. The success of that is measured by my first statement.
On topic though, the '88 issue is a victim of the game character...IRL, those AA mount '88s were in depth, and primarily intended to engage aircraft, and used in the ground AT role in emergencies, more or less. When they carved up a fair chunk of Goodwood, they had to be ordered not to engage aircraft and to take on the tanks...and they did so at long range. We don't have that long range in game terms, for the simple reason that all direct fire weapons engage under 1200m. That saves allied players on broad and more open maps being shredded before they get part way across the map, it also means that we see a mass of AA units appearing in the front line, when in reality that was very unlikely to occur, notwithstanding that they aren't concealable like AT guns.