You are surely overstating things by saying YHWH was the most cruel god.
It's been stated somewhere in WT literature that the gods of other nations were much less perfect in their ways (more like imperfect humans) and less omniscient (almost as helpless like us) than YHWH. If that is true, then YHWH would be one of the most cruel gods.
You would not call a lion killing a zebra cruel, but seeing killer whales have fun with sea lions might make you wonder. The notion of cruelty somehow correlates with intelligence and other capacities.
In the human world just turning your back and leaving someone to suffer and die if you could help him is considered to be cruel... how about in the world of gods?