BAR, they aren't as uber as you think. Honestly, 90% of my tricks involve getting in on flanks and behind them. I've taken out 2 tigers this tour (might be listed under last tour, was near the start of the month) with an M4A3(76) by circling around on their flanks, while others were trying (unsuccesfully I might add) to rush it, and get within effective range. Thats pretty good considering your notions of GV combat.
And honestly, no defense (short of CV manned ack) will stop everything. And there is JABO fighters too. I guarantee that a 1000lb bomb on top of an elephant will stop it. It will require good accuracy, but thats rarely a problem in the MA's. There is always an abundance of talent flying around.
Personally, I would be perfectly fine taking on an elephant with a panzer or an M4A3(76). Just so long as I have cover, and he isn't actively hunting me.