When I play Germany, I can win very easily by making massive tank attacks, as you tell, in G5. Infantry, infantry, then TANKS and TANKS and TANKS…
When I play Allies, with UK and US i send to Russia at least ONE fighter per turn (one with US and one with UK) every turn, plus the two bombers they got at the begin. With Russia I’m not passive, but I make “soft” attacks. I send ALL I can against a Geman territory, I conduct one or two rounds of fire and so, when I’ve destroyed almost all his infantry, I retreat and then I reinforce the territory where I’m retired during non-combat phase. Usually, this tactic can slow Germany well.
But, in effect, when I’m Allied my friend (that’s my opponent…) doesn’t love to make massive tanks attacks, he tells it isn’t funny… So he buys a lot of infantry and subs too and he plays defensive! Funny, maybe, but not a winning style of playing…