My thoughts on the two teams:
Like others think, Aether is probably secretly the true evil organization for these games. Team Skull really just look and act like punks. If you think of real life Hawaii, there are locals that aren't kind to people from outside of Hawaii. Team Skull could really be a reflection of them. Aether is taking in the "stolen" Pokemon and protecting them only to save face with the public, while really they are experimenting on them, in an attempt to create their own Pokemon, the Ultra Beasts. Type: Null was a prototype and was too Pokemon like for Aether's goals, and thus wanted to get rid of it, causing Galdrion to take it, run away and join Skull to stop Aether. Guzma just wants to be a trial captain and Plumeria looks to care for the Skull grunts, neither of which look to be what an actual evil/nefarious groups.