GMAT Sentence Correction (SC) | Re: The European Economic Community exported just under $400

Yes, you are absolutely right. In this example, if the second verb were "has"/"have" ("...as the Japanese have"), then the point you have mentioned would be applicable (this would then be a case of omission) - since there is no past participle ("exported") form in the first part of the sentence, using "have" would be wrong.

However the simple past "exported" can be replaced with "did". (This is not a case of omission.)