Nonsense. Not only are there genres that are specifically built around particular synths (ie, Acid and the 303), but there’s also clearly synths that specialize in particular types of sounds and are weaker in others. Not all synths are all ‘rounders. For example, a JV-1080 wouldn’t be a great choice for someone wanting to do dark, twisty DnB or Dubstep basses. And its worth saying that just because two synths are capable of similar genre related sounds doesn’t mean there isn’t a difference. Of the the subtleties of character makes a certain great in some roles that a similar synth doesn’t do quite as well. They don’t all have the same features or focus, and it’s not all in the way you program it either. Sometimes a certain synth is just better at certain sounds.
Your argument is like saying that any guitar can play any genre. While technically true, some guitars are built with certain genres in mind, and work better for those genres. That there’s instruments (both hardware and software) made for specific types of sounds shouldnt be a controversial idea. It’s fairly self evident