In my experience the lack of meters does absolutely nothing to prevent the toxicity you're talking about. It just allows more people to be toxic due to no one actually knowing how well / poorly they're playing.
I remember playing swtor back before people started using the 3rd party programs to get in game meters and people acting like they were gods gift to the game and all the same toxicity only for the meters to tell a very different story once people got around to using them.