One way in which something can be legitimately dumb is that something is hard to beat AND autopilot as shit. Like, let's say your chara has a 16F safe overhead they can gatling for free. Why would you ever /not/ use that shit? You could autopilot it all day and beat people into the ground, and just run unreactable 50/50 high/lows in the middle of your blockstrings all day.
A good example of a legitimately dumb move was CS2 Tsubaki's D Shield Rush. It covered shittons of space, practically anti-aired anything in its way, and almost always traded in your favor -- and if your opponent blocked, you were plus. Once you had one charge, every chara had to suddenly watch out for it and respect this fucking massive amount of space. The only thing that kept it from being completely and utterly stupid was the charge cost.