I had a mel and it was never a problem. Kept with scopas yellow tail damsel, Toby puffer, cinnamon clown. I briefly had a leapord and there was slight aggression nothing serious. It wasn't what killed it.Interesting, in my own anecdotal experiences of other friends keeping melanurus wrasses, they never seemed to have issues. Tbh it's on the bottom of my current wrasse list so I can prob axe that and include something else.
Crabby is a wrasse expert. I'm not sure how well it would do with other wrasse. In my brief time with the leapord I'm not sure how the aggression would have turned out.