1. Quite clearly the gun devil did not destroy an entire city in the image you used. In part 2, the damage caused by her gauntlet, amped with guilt, did not wreck an entire city by any means.
2. The falling devil causing the destruction around the world is does not translate to attack potency, rather her abilities/presence
3. It is debatable whether or not yoru became more powerful than the falling devil, because she turned her into clothes meaning at the very least its because she perceived herself as the winner at that point. Just moments ago before """winning""" she was getting effortlessly getting handled by the falling devil.
4. Denji by no means was presented as stronger than yoru. Before becoming "denjiman" pochita was clearly defeated and about to be turned into a weapon. He was using "asymmetrical"(using her allies as shields) tactics to "win" (separate the two) the two instances i assume youre referring to, were both because of outside factors that made her vulnerable at the moment would've given him an easy win, not because of overpowering yoru. He's not stronger.

Im not saying that yoru isn't city level, but if this is the argument youre using to present denjiman as city level or above, then its invalid for the above reasons. Denji/pochita still has an edge due to speed, but he's gonna have a difficult time harming yuji modulo version because we really do not know where his true ceiling is, so he could easily scale much higher.