I honestly don't care about those technicalities. No matter the first or the latter, they are both working "together as a single being." That's Double's thing alright. So it's fine with me, beside, the final form ended up sucking from what I'd seen although I try to avoid them spoilers(and I do 99% of the times).
Shroud turning into a villain isn't far fetched, it's actually called "plot-twist" if it ever happens, though it is fairly regular in mystery type genres. Often, the masterminds are those whom you least expect.
I just realized that the Weather Dopant is Cronicle Asher from Victory Gundam. Also, my wife pointed out that he sounded exactly like "that shark guy from Naruto" (Kisame).