I find Lend-Lease cheese to be good against OKW.
DShK HMG in buildings do miracles (instapin? Instapin!), as they alone are the best HMG's in the game IMO, and with AP rounds ability they can even kill a Luchs. Flanks are easily locked down by a couple of cons+guards (if you want, you can make a Quad out of M5 call-in). And a couple of M4C Sherman's are a nice choice to battle with OKW late (except KT). Good cannon, pretty fast and fast to repair because of Cons repair abitily.
You'd have to be EXCEPTIONALLY bad at the game to lose Luchs to DSHK. MG42 incendiary rounds are much stronger and reliable then DSHK AP rounds. The ability doesn't even do good damage to Puma frontally.
M4Cs are good, but they aren't competition for OKW P4 or shreckvolks.
Con repair is useful, but cons who repair don't cap(because you certainly can't use them for fighting in mid/late game) and their repairing speed is something you don't want to resort to unless you reinforce and heal at base.