The single button smasher IS the cruddy tank or healer though, the button just changes to the AOE heal or the flashiest Tank skill instead of the big numbered one for DPS. This is OP's concern. Someone who thinks this is how you play (SMASH DAT BUTTON!!) and anyone who suggests different is elitist or playing the game like a job.
These people aren't going to calmly sit there while you push numbers at them. They're going to yell "YOU DON'T PAY MY SUB" and then report YOU for harassment. They've never read a log, they have NO idea what their DPS or HPS or Threat generation looks like and wouldn't respond to those values even if presented with them.
I don't deny parsers are a valuable tool, but in this case, as in the people the OP is referring to, they are not helpful (and partially I don't think this thread will benefit from the pro/anti parser discussion that always comes out of that) for the type of player who learned incorrectly or refuses to take advice. I'm purposely going to avoid any discussion on the pro/cons and just say in this case it would not benefit anyone to bring it into this interaction.