It's likely that the issues with DES would have been discovered sooner had they not been fixed, after all an actively used system is far more worthy of study than something thats been superseded and is no longer used.
That is nonsense. The fixed DES was identical to the original DES, with the expectation of a couple of seemingly arbitrary numbers. Nobody's going to stop researching DES because the NSA changed a couple of numbers. In fact, the opposite is far more likely.