I'm not referring to Ulanoff specifically, but come on, let's not be disingenuous, you (I assume it's you, correct me if I'm wrong) using him as an avatar of the criticism Masto was getting at the time. He made a maximalist prediction and was wrong, so he's a convenient target to act as a dismissal of the genuine concerns being raised in general when Masto got into the mainstream's focus.
Notably, he wasn't entirely incorrect. Thousands of people did move on. I did. I'm not writing this on Masto. Did Ulanoff miss the fairly obvious point that with no centralized infrastructure Masto is actually more viable when it's small than when it's large? Sure. Was he right to claim that it was "less Snapchat than Path"? Sure. Arguably whoever remains at Masto is perfectly fine with that, and that's cool, but at the time the debate was whether Twitter would be replaced by Masto, and that did not happen and will not happen, in no small part for the reasons more sharp-eyed critics than Ulanoff pointed out at the time.
It's a bit of a tangent, but to interject my own take I'll say that Masto isn't even on my top 3 for AP applications. Twitter is just not the right format for the way AP works, Masto is not a good implementation of Twitter and some of the technical shortcomings Masto users keep insisting don't matter actually do matter.