Isn't the Imp Gang Boss just a reworked Imp Master? And nobody runs that in constructed. I guess it having 2 attack and being a demon makes it slightly better.
2 attack makes a world of difference. Having 2 attack is more than twice as good as having 1 attack. You can't really make trades with 1 attack. And with Imp Master you only get good value in a "win more" scenario where you are already ahead. Imagine using this as an answer to a 3/2. You'll get a favorable trade plus two imps. This is also a pretty good answer to shielded minibot or a 2/3. You'll probably get 2 imps guaranteed. Or maybe you kill the mad scientist and use the imp to trigger the freezing trap.
Another way to think about it is compared to Harvest Golem. Imagine if Harvest Golem was a 2/4 with a deathrattle to spit out a 1/1 OR two 1/1's. That's pretty good. I think this makes a lot of sense in zoo because it's super sticky that way too. They're going to have to try and kill your imp gang boss first before doing any AoEs, kind of like the awkwardness with haunted creeper, but here it's even worse for your opponent since it has 4 hp.