While I would not reject the idea flat out, it seems a bit unlikely that a (global) flood managed to reach such height and submerge the pyramid for long enough to impact the rocks with sea erosion.

I'm not a geologist but I would assume it would take decades or centuries to cause rock erosion. And then the flood would just vanish somewhere I guess.

It doesn't really seem like a theory that I feel compelled to consider. I haven't looked at the video so perhaps I have missed some point or misunderstood the thesis.