That's fine in theory but 2+ ISG + Med Truck + Flak Truck. No amount of flanking will save you. Want to counter it with artillery? ISG shoots farther than everything else. Once dug in they require very minimal effort and that's the problem. Doesn't help that USF and Brits have few artillery options to begin with. Secondly if you DO get hit the suppression lasts long enough for 2nd and 3rd shots to land and due to the high accuracy now its basically an auto-retreat.
Obviously, if they have a flak HQ then it's not really viable to flank. The idea is to put immense pressure on the OKW player and to get more map control/resources so you can get vehicles out much faster. I should note that I almost always incorporate a sniper into my build when fighting OKW players.
People are definitely over exaggerating the projectile speed of the ISG. If you take a shot with your sniper, then move him there's absolutely no way the ISG can hit your sniper; I've done this in all of my 1v1 and 2v2 matches where I simply wear down the OKW player with my sniper while using an infantry section or two to screen any infantry advances, while my other units cap around the map.
If this thread is still running a week-ish from now I'll post replays of me beating high ranking OKW players as the British just to prove my point, and quell these statements of the ISG being OP.