I think it's more because most people are bad at this game and 29s have a disadvantage with their health/damage reduction. Unless you are an absolute beast I won't keep you in our fireteam. I'll let a 29 in but after about 6-7 consistent deaths before anyone else, you have to go man. I've seen a 27 do Atheon and wreck face with us but he was amazing so I expect nothing less from a 29.