Mearls is likely to say it's a flaw of 5E as well. You end up making playing the barbarian more about the player's maths skills than the fantasy of being a barbarian.I'm about halfway through the interview. I feel like Mearls is overstating how much more tactical 5.5 is than 5E and how much more people are focusing on builds when in my experience they're about the same. The mention of monsters doing more than one damage type with an attack as a new 5.5 innovation is odd to me as we had creatures dealing multiple damage types from the 2014 Monster Manual itself (such as the vampire's bite). I will give him that tying feats to backgrounds was a bad idea (though thankfully easy to homebrew away), but as someone for whom weapon masteries was the most exciting new innovation in 5.5 I'm very much opposed to the idea that it creates unneeded tactical complexity (my second 5E PC was a battlemaster fighter/hexblade warlock with pushing attack, repelling blast, and grasp of Hadar, so another way to push enemies is very welcome).
(He has certainly been candid about the flaws with the 2014 MM & CR design).
Cheers!