Wicked gods are nothing new. There are some of them in cultures with multiple gods. As to whether their actions can be called sins, probably not. The concept of a god committing a sin against humans just doesn't match the idea of what a sin is. Neither does a god committing a sin towards other gods (underhanded pranks, crime etc would be more fitting since multiple gods also usually tended to be arranged in some sort of hierarchical society among themselves).
The Japanese Shinto god of the seas and storm Susano-O is pretty fitting of that, for example. Did some nasty stuff to other gods, was punished but not because his action were a sin or wrong, but because they were hurting and disturbing them (pranks/crime alright).
The Japanese also don't seem to have a big flood myth, although no doubt they've had a fairly large share of floods with the nature of their islands. Maybe a consequence of having the sort of god reign over those calamities who wasn't all good and nice and was prone to go a bit berserk without needing to punish anyone.
In any case, like it's been pointed out, "global" was a fairly narrow term for people some couple of thousands years ago. The sort of "global" that we'd call "local" nowadays. Plus it's absolutely certain there hasn't been a global flood anywhere close to those periods that myths deal with.