He's not saying anything that people in the industry don't already know, that was basically his point. I will say that he's wrong about two things though: 1: Twitter is an effective medium for communication, 2: character development is done in separate scenes versus characterization.
One thing that was clearly lacking in American Ultra was the lack of proper characterization, where the actors had just one aspect (per character) to work with versus the multitude that a fully fledged character should have, and couldn't really do much more with them. Either because there was no time, money, or the director didn't see that, whatever. I'm not willing to buy completely into a fairly typical "there is a system of hacks, therefore anything goes now!" type reasoning. A better writer tends to create better movies, even under the studio system. Hacks will still produce successful hot garbage (see given examples of TF4 and JW), but not because nobody ever tried to make something slightly better out of it.