How about redefining the problem a little bit so that it is something else than what others are doing?

For example, the platform approach? Allow people to easily set up a temporary email service with their own domain. That would go around the problem needing changing domains all the time. You could make it easy for people to search and buy their temp email domain through you.

Or if that is too much, work, allow people to self-host your service by open sourcing it and creating Docker compose configurations etc.

I would personally also write a spec for one-click account delete link that can be recognized automatically, sent with the email. If that takes traction, then it would benefit everybody. It just might, as it benefits the service provider the most.