No it wasn't it could do great things. You just had to find the right patches. And running it through some outboard effects can really make it come to life. It had some of the best velocity sensitive patches that really responded well to playing dynamics. In my opinion much better that most modern romplers.

It just didn't have the ability to make analog synth type sounds, though later versions of Yamaha FM such as the SY-77 could do that much better than the DX-7.

It was the first affordable digital synthesizer and made history as well as featuring on many hit records in the 80s. Plus nowadays there are more free patches online for it than any other synth. It may be awkward to program but a least there are many 1,000s of patches that may be a good starting point to tweak.