I disagree that Viper is complex, it is one of the simplest melees in practice, and the extent of its complexity is having the worst worded tooltips ever made. I have a few minor critiques toward the job, but mainly, rather than having a reduction of positionals, I think the better solution is to stop making the same buttons turn into different positionals, because I think an overwhelming majority of people have mapped attacks with positionals in certain patterns for other melees before Viper existed. For me personally, flank is top row on the hotbar and rear is second row. I play with MMO mouse + keyboard.

That said, I agree with most of what you said about the job being mostly fine that it's not made for everyone.