Man this game about a war is...about war? Man who woulda thunk it. I mean not to be too snarky but I feel like the first third or so of the video was just trying to hammer in points that I thought were pretty obvious. The game's not really that subtle about its war themes, it's just that none of it lands due to poor writing and being played out by silly cartoon forest creatures.
Also I don't think Tails was ever actually meant to be on par with Sonic in the classic games. Tails alone playthroughs aren't canon. I'd say what Tails is supposed to be in those games is closer to what you see from him in a Sonic & Tails playthrough (though probably not quite as incompetent as the simplistic AI); he follows behind Sonic, he sometimes bumbles into traps and enemies, he can help out occasionally, but ultimately it's Sonic doing the real work. I do agree that the games from SA on focusing on his unique strengths rather than him being another Sonic is the right move though.
As for the actual subject of the thread, I'm not sure if I'd call it capital-D Depression, I'm neither a doctor nor do I have depression myself so I'm not sure I'm comfortable reaching for specifics like that, but they were definitely starting to do a thing where Tails was seriously affected by all the shit that had gone down. It doesn't ultimately work because, as you said, they immediately drop it, but Tails cowering at Chaos is clearly not meant to be Sonic Team or Pontac and Graff or whoever declaring that Tails sucks now and is a dumb cowardly baby because they hate him. The kid watched his best friend get the shit kicked out of him to the point that he's presumed dead, and he's gone through six months of watching their worst enemy take over nearly the entire planet; it's only reasonable that that'd leave some marks. As much as there is to criticize about all this it's frustrating to see it get written off as just bad writing or some kind of anti-Tails bias, especially when so many people are also hoping for the series to take itself more seriously. Like, more than Infinite the edgelord, more than Sonic being serious and not telling jokes, this is the series trying to do something meaningful and significant with one of its characters, and yes, it failed, hard, we all agree on that point, but I still think it's worth recognizing what it's trying to do.
I mean if people are willing to give Infinite another chance for his supposed potential shouldn't this at least be acknowledged?