If they won't leave straight after campaign, they will leave when they realize that
a) the amount of bugs in the game and new bugs being introduced with every patch
b) balance is so bad
c) small playerbase causes relatively many unfair matches between differently skilled opponents
d) the multiplayer units behave totally differently to the campaign units
Indeed at least the OKW panther is a bit ridiculous with it's nascar blitz and overall better performance compared to the Ostheer panther. Have you tried jacksons and IS-2s? The IS-2 can take quite a bit of beating due to it's high frontal armor while the jackson has very good penetration (especially with AP shells at vet 1) and can take shots from a safe distance.
Considering the game mode is 3v3 or 4v4 it is to be expected that there will be lots of late game tanks. Especially since the fuel caches also benefit the OKW players. Have you considered trying 1v1 games?
If you have a big advantage, you can try to skip the halftrack and save the fuel for sherman. If you can maintain your advantage and skip the halftrack you can have the sherman out at 11-12 mins. It's a real pain in the ass especially for the Wehr player.
Go to Games -> Activate a product on Steam and insert the cd key there I think Steam doesn't ask the key, you have to do it manually. That's how I installed the original Company of Heroes that I have on cd and it worke just fine.
Some regular green cover providing objects, like the stone walls on Semoskiy sometimes don't give you the green cover icon for some reason. Don't know whether the cover still applies or not though?