Normally it would be just a... trailer. When they put Gameplay Trailer on the title, you expect a lot more than what they showed.
So, yes, they should have just called it "Trailer".
But also... get used to it? Game companies have to title their Youtube footage in a certain way to best meet YT SEO, and putting "Gameplay Trailer" will sort better and connect to "Game" recommendation systems better than the generic term Trailer and generate more views overall, especially given that there are multiple R&C Rift Apart trailers already in the system. Ideally, they'll title it in a way that's best for gamers as well as best for the Google spiders.
This one's not a crime. There's lots of gameplay in there, it's a gameplay-focused trailer instead of a story or character trailer (they might have called it the "Rivet Trailer" since she's a big part of it, but then maybe we'd be having these same 90/10 arguments since Ratchet's in it more,) there's going to be an entire Showcase in 3 days that'll be full of live gameplay, it's called a "Gameplay Trailer" not "Gameplay Showcase" so that already indicates that it's cut for the Trailer experience of best-of clips rather than a detailed display of how the game plays, we've already seen the game running in gameplay, and really, the only thing wrong with calling it "Gameplay Trailer" is that you had different expectations from the video title. Seems like one problem is easier to fix than another?
I get maybe you're trying to protect from. (I was pissed when Nacon had the balls to call
the newest Test Drive Unlimited Solar Crown video a "Trailer" when they've gone two events now and haven't shown a frame of footage,) but nobody's being ripped off here. It's a click to free content, and it doesn't clickbait you into something it doesn't deliver in the title (maybe not to your full satisfaction, but there's no pleasing everybody.) They showed the game being played (for the third? fourth time now?,) and they will show more real soon, and if you didn't get enough gameplay in the Gameplay Trailer, come back Thursday.