Any suggestions? (Short of let people do it).
This goes for clarity, difficulty and size of the task. Don't make someone bad at filling the details do an unclear task. Don't make someone unskilled do a clear yet difficult task. Don't make someone with no track record work on a task for too many days without supervision. Etc.
Unfortunately, people not meeting standards you would will always be a thing unless you're leading people more skilled in the area of expertise. Which brings it's own set of issues.
Delegating is knowing that you need to let go and ingest the fact that they are there to help. Mistakes happen and will happen. But that is part of learning for you and them. If they are not learning that is a different issue. Do not worry about it. You will learn what you can put them on better. But once they learn something they can turn around and help you learn. They can take care of it and you do not have to worry. Delegation is trust. Learning to trust is learning to 'let go' and being open to being 'hurt'. But also being willing to forgive and forget.
What seems to work is where areas of the product are assigned to specific teams - the overly-attached dev can at least see what's happening, provide guidance, without having to do the work, point to wiki that needs updating etc. Over time they'll build trust and can back away a bit.
What doesn't work is if work is given to a different team who just do their own thing and the 'parent dev' only finds what's happened to their baby on the commit/demo. Even if they've done a great job, it ruffles feathers.
Unless you can change that trait, it's going to be a hell of a bumpy road with no payoff.