You can definitely delete stuff. It doesn't work really when clients decide to broadcast your content to dozens of hardcoded relays, but in a setting where you're publishing only to one or a few handpicked relays as in the scenarios I described deletion would work perfectly. The "you can't delete" stuff is more a legacy thing from 3 years ago when everybody was committing all kinds of sins when making clients. We're not perfect yet, but much better. Many clients already have a button to delete, others should implement that as soon as possible.