Romulus isn't allowed because his np he's not allowed because imperial privilege ex is literally any skill on demand without drawback like nero's headache and then even better. Romulus is flipping strong and he had none of hero's drawbacks. He once took presence concealment and hid three people in a whole parade and then walked into the Roman palace with them. Benkei isn't allowed be side his phantasm steals phatasms gg lancer you have no lance and no luck to fight it.

Alchemy is judged on a case by case basis and is limited by how much stuff you carry and can be based on that also rin and kayneth  are high tier mages run gas all affinities and kayneth has years of training.