Sorry, but I'll have to disagree here:

The 88's made their debut as AT-weapon at Arras in 1940.

The advantage was two sided:
1)The 37mm gun on the Pz.III was useless against the heavy French Char B series, as was the 75mm L24 gun at long ranges. The armor piercing granate of the 88mm FlaK gun had no problem with penetrating any French tank.
2) The incredible range of the 88's. With a firing speed of 20 shots per minute and a effective range against most tanks of upto 2000 meters it was capable of destroying enemy armour on the wide plains of both North Africa and Russia and the enemy could not fire at them.

Thus it was not a question of using everything available. It was simply the most effective way to destroy without being killed. Starting in 1940 the FlaK crews where equipped with sufficient AP-ammo for their guns to be fully operational in their role as AT-support.

As for why they didn't use the 90mm AA guns on the American side for this purpose:
well, thats the Allied logic of that time. Why stick to Shermans is a similar question.

But keep in mind that by that time the Allied Air power and Artillery power was sufficient to deal with most German Panzers.

Just my 2 cents,
Timo

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