I was having a discussion the other day with somebody who said if they want to raid in Legion, they feel they HAVE to run Mythic+'s. This thread isn't about if Mythic+ helps gear up toons (it obviously does), this is more of if you feel they HAVE to be used to get a toon raid ready.
My personal opinion is that they are NOT mandatory. Yes, some trinkets from the mythic+'s are simming as BiS for certain classes, but by no means would I ever refuse to raid with a player because they didn't have the BiS trinket. I realize I also don't raid at a top level, but for him to feel left out because he doesn't like running Mythic+'s (he has anxiety and they cause him a lot of stress) seems like an unintended consequence.
Again, my character has only completed ONE m+15 and I barely run them once a week (if that) and I'm still at a 926 ilvl 8/9H ToS in a guild that plans on moving into mythic ToS and I do just fine parse wise.