Animation in general suffers from CGI characters not seeming to have weight, but I think the main issue is that a lot of the new animators have come from a traditional weight/space/momentum mindset.
The RWBY characters aren't supposed to move like they're jumping high, or like they're weightless. They're supposed to be propelled through the air like they've been shot out of a cannon - it's the recoil of their guns, which is why Monty had so many of the weapons be guns in the first place.
Weiss is just moving too slow in this trailer, and all of the Volume 4 fight scenes seemed to have this problem too. The weight and speed is what gave those scenes such intensity, and it was so insanely and creatively choreographed, especially when it was one-on-one fights.
RWBY is definitely different and I'm glad the show keeps moving forward. It currently looks gorgeous, way more than it ever has. But the choreography still seems off to me. I'm not sure if it's purely just in my head because I consciously know Monty's gone. If I'm being honest, I thought something was missing in the RVB Season 10 fight scenes too (except for Tex/Carolina vs Connecticut/Rebel Leader).
I spent so much time watching Dead Fantasy, Haloid, RWBY and the RVB Season 8/9 scenes fights at 0.25 speed on my computer so I could see how the choreography took place almost frame by frame. This new RWBY is very, very close, but it is missing some choreographical magic.