"Did you try to find out why was the landuse mapped this way before declaring multipolygons useless and mass-converting them?"

That's one the reason why I started this discussion and my theory that you find it easier to edit with mps was confirmed.

This method might be an easier one for you but don't you understand that other editors find it very hard to edit the section in the map you were editing after you, especially iD users? iD editor is quite restrictive, it will straight up prevent user from doing actions that may or may not cause errors, like disconnecting members of a mp or performing actions on an element if it's not entirely visible. That's annoying, but iD is intuitive and modern, interface is visually appealing. That's why I use iD for mainly simple tasks. But randomly comming across areas mapped like multipolygons which I want to edit always makes me sigh and open JOSM to deal with them and then return to iD to finish what I started.