Given the roadmap says "More to Come Based on Player Feedback" and this is player feedback it's 100% valid. I'll add on that the roadmap doesn't currently say there will be more augments in the future and that's something I'd like to see.
I don't understand the stance of "there's no need for it." It's a game. Games are about fun. If something would make the game more fun then why not? It's also silly to say the current roadmap has significantly better ways of expanding the game because the time frame on the future is indefinite, so OP isn't saying that they don't want the other things, just that they would enjoy the game with more bindings. If they had said "New augments should be the top priority in development" then you'd have a case to say that the current prioritization is better, but that isn't what they said.
I'm also lost at how you can say "there isn't much design space." The whole game is design space. They could do anything they wanted including adding terrain to combats, status effect combinations, summon minions, etc. There's an unlimited number of things that can be done that are only limited by what you can think of.
These are just my thoughts, but I don't think it's helpful to tell people why they shouldn't have the opinion they do with this kind of logic, especially when the roadmap specifically asks for player feedback.