Technologically, eSIMs are pretty nice. The electrical interface between the phone modem and the eSIM is the same as with a real SIM card, and the eSIM can run the same applications as a real SIM card, so at this point you can buy smartcards that can be swapped between devices and run eSIM applications. esim.me, 9esim and the "sysmocom eUICC for eSIM" (seems to be the most open/friendly at this point) are some of the options. Most of them offer an app for management, but there are also standardized interfaces.

SIM cards have always been secure elements that the provider trusts. With an eSIM, you can already own that secure element and the provider can provision it with their application. You can even have the applications from multiple providers on the same physical secure element.

The major advantage is now that the expensive and time-consuming part of provisioning a new mobile service (sending out a physical SIM card) can be replaced with a few standardized API calls. This is cheaper (which makes the extra cost some providers charge for an eSIM look quite silly) and a lot quicker, which enables new business models for short-lived cell connection services.

A world where all cell service providers offered eSIMs would be slightly nicer. But manufacturers removing the option of swapping the secure element is very annoying at the same time.