Yes and no. Unionization would result in unions negotiating against Uber independently. As the dominant player I can see how unions would negotiate harder again

Yes and no. Unionization would result in unions negotiating against Uber independently. As the dominant player I can see how unions would negotiate harder against Uber than (say) Lyft. A law would mean Uber/lyft/etc. would all have the same playing field - which is better for Uber.