The German Tank Ace Michael Wittman started out and made his name in the East Front commanding Stugs. He didn't use them defensively either. He hunted and killed Russian AT guns in his.

And then they gave him Tigers.

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But -- this thread is about WWI.

The Schneider, the St. Charmond, the Brit Marks...

And nobody had a good AT plane, did they?
Unless you count recon planes coupled with arty?