The reason 5E has some narrow classes is essentially cowardice.
They were too afraid of being tarred with a 4E brush, so instead of being willing to deviate from how classes traditionally were, several of the classes are basically just "throwbacks" to 3E, and very narrow and odd as a result. Sorcerer, Druid and Ranger are - I'd argue Monk also was. Bard is remarkable in that it is absolutely not a throwback to 3E, but a genuinely bold decision with mostly-novel abilities. And they seem to be much more popular in 5E than previous editions.
If they'd done what they did with the Bard with Druid, Ranger, Sorcerer and Monk, I think we'd be in a much better place. Druid and Ranger might have merged, with a slightly more developed Nature Cleric taking over the "pure caster" Druid, and a Fighter subclass taking over for no-magic Ranger via a subclass (with more skills etc.), and we could have got a class with subclasses that let it end up as focusing on either being a warrior with some nature magic, a partial-shapeshift warrior like a 4E Warden, or a shapeshift-centric character. The class design could have been Warlock-like.
Yeah I don't think his thinking is that advanced. I think he's just making very basic observations of a trite kind. However, we're both reading in from an interview where they didn't drill down on this, so it's hard to really say.