You can't px scale something coming towards the screen like that and Izuku was a good deal away from Mount Fuji as well, he wasn't exactly at the base.
You would need to angular size a shot like that and there is no way to get the width using that shot.
Also, it's assuming the depth is the same size as the width, since they're treating it like a cylinder, which is incorrect on both fronts. The shockwave expands the further away it gets from Izuku so it'd have to be kind of triangle shape, not a cylinder.
We do have this shot of the city behind them,
which has been completely destroyed.
A quick calc of this is giving me
7+ Megatons of TNT (
7-B). Kind of fits since that did destroy a city.
I think this is the most destruction Izuku has ever done as well, and this was just him flicking with all of his fingers.
He'd without a doubt could kill Tomura in one shot if he punched him with that kind of power instead.
If the attack did cause the amount of destruction in the blog you linked, all of Japan would've been destroyed. That completely breaks our KE even if the px scaling was correct.
Edit: Though the speed is incorrect, that timeframe would only apply to when the attack hit Shigaraki and not the full attack.