… that’s a bit like telling the person asking for directions “I wouldn’t start from here if I were you” 
The relevant JOSM help is. I think, this but personally if I’m validating relations with JOSM (which is quite often) I always hop over to Potlatch 3 to do the actual edit because the editor is a lot more understandable. However, there should be no need these days to leave any particular editor just to perform basic relation management. The exception is features (like validation) that JOSM supports, but other editors don’t.