True - my point was that the carrier can't prevent you from physically switching SIMs and locking them at the network-level to an IMEI would cause backlash as it would break long-established conventions.

With eSIM, not only are they in control of switching eSIMs between devices but it also gives them a clean slate to introduce the aforementioned network-level restriction under excuses such as security (though again since they're in control of switching eSIMs they can just block it there or be annoying in other ways - some carriers already charge for reissuing eSIMs despite it being a completely automated process).