You're assuming too much frenchie. I'm not against change, but not liking the way it is already handled is another thing, and that's what exactly you and others are saying.
You just need what you asked:
- Unhide only ONE specific message
- Show all hidden messages in a folder (to select the one that the user wishes to unhide)
- Decide when to permanently remove hidden messages from the device
There is a feature request forum section. Go there and post your request. Kostya will add it to his list and decide when to do it.
And again, the post was about "How do I not delete mail from server using POP account. If I delete from the Deleted Folder, the message is deleted from the server."
That has a simple answer in AquaMail, "Hide in app, keep on server". That summermug doesn't use this feature and you don't like it, it is another problem.