So the Set kidnapping Allomancer is not about making Inquisitor, it's good old disgusting human trafficking. Allomancer for Aluminum? That can explain how they seems to bounce back so fast after AoL.
About full-out WW, I don't think it will be possible, if it happens it will be more like German occupation of France but much more brutal when Allomancer and Feruchemy throw into the mix. Elendel techonology might not full-blown industrial age but they are advanced enough to put out sniper rifles, automobiles, explosives. The only modern thing they lack is landline alothough that will happen soone I think if Aradel want to expand into the Roughs.