Linked this post in another thread before, but I think it summarizes the problem pretty well.

I'd rather its total potency match up with dosis at the least so it can act as a niche mobility tool in single target than be a dps loss. It'd still function as one even if it is slightly a loss but then it's kind of a worse Ruin II/Toxicon at that point.

Also you'd still have to manage it when there's 2 targets, which makes me wonder if FRU phase 4 might've had a part in why they chose to not let them stack.