I dunno what exactly he did, but him applying the anesthetic sucked way worse, but I didn't feel anything whatsoever during the root canal itself. So I'm definitely asking my regular dentist next time if he knows of any anesthetic methods that involve injecting it really slowly and it hurting, and if not if he could maybe have some conversations with his colleague about that.
So I guess nothing super helpful, other than the knowledge that the way the anesthetic is done has a LOT of influence on how well it works.