I prefer generic, as do most of my players. Given our frequent play (1-2 fairly long sessions every week) and our play-style (all dice rolled in the open, no fudging, death-or-glory), we go through a lot of characters. Close to 50 since 5e began. And the fighter is the most popular, by a considerable margin.
As has been said by other commenters, the flavor of the other subclasses can sometimes actually restrict the creativity. The monk is basically Bruce Lee, a ninja, or an elemental bender (i.e. Avatar). There is incredibly strong flavor in all three of those sub-classes. But the champion fighter can be anything, depending on simple Background choice. Pirate, mercenary, town guard, soldier, gladiator, knight. I've seen all of these, simply from the champion fighter. My players aren't unhappy with this. You don't need mechanics to model every single subtype; you simply need enough flexibility to differentiate characters. And with Backgrounds, Feats and Combat Styles, we already have that.
So, I really don't think Mr Mearls should feel too disheartened. His team have done extremely well by my group. We think the fighter is one of the best and most flexible classes in the book, from a roleplaying perspective.