PDP can and likely would take them to court and I imagine he has more money than they do which would present an unfair case in terms of fair use especially with that statement they made about streaming.
They're probably in the right morally, but they're likely screwed legally.
Legally, this is really murky ground, and right now everyone involved benefits from it staying that way. If I can't post a full movie with my commentary over it (why Rifftrax is audio-only), why should I be able to do the same with a video game? Is your gameplay actually that transformative? I could go into more detail, but at the very least this isn't clear cut. I'd be shocked if anyone goes to court about it, because if the Youtubers lose, then their entire niche vanishes overnight.
From a less legalistic point of view, the harm that comes from developers/publishers posting takedowns of Youtube videos about their game depends on how the audience sees what they do. If you're using DMCA notices to suppress criticism, then naturally you're going to look like an asshole. I don't think it's hard to draw a hard line there.
If you use DMCA to prevent your game being associated with political viewpoints you find abhorrent, then there are going to be some people that cheer you on, and some that find the action to violate free speech principles or whatever. As a developer you insert yourself into a very polarizing argument, and if you're comfortable with that then go for it.
I generally feel like people should be pretty free to share and remix work, and I don't like Youtube's DMCA system because of how sweeping and arbitrary it is. But I also absolutely understand that someone might not want their creation to be used in a way that associates them with ideas they dislike. Other content creators should respect those sorts of requests.
