The way they were infuriating motivated the player and makes it satisfying when you beat them, so being annoying was absolutely the right choice. The last Pokemon games I played were on DS where your “rivals” were nice and supportive and non-annoying and they were boring and I would have fastforwarded them if I could have.
Each account has an allowance of five devices, although you can de-register and re-register devices as much you want, it only takes clicking. So yes.