The SIM is just an identifier. There’s nothing particularly special on a SIM card, that’s why the switch to eSIM has happened so seamlessly. So, you’re right; it’s totally POSSIBLE that an eSIM could stick around if you delete. But it’s also possible that your phone could save the info on a SIM card.

For the record, I don’t think that’s likely. Your phone’s operating system (iPhone or Android) is built by a different company than the carriers that presumably want to track you. I doubt they’re secretly colluding with carriers, because Google and Apple already have enormous business models built around tracking you, and profiting off your data.