The vortex caused by the vane is incidental, it's main purpose is to move air out of the way of the main air jet coming from the diffuser kick line. The two counter rotating vortices entrain some of the air that leaves the floor directly behind the plank.
The vanes add performance, to be sure, but they seem like a patchwork to make up for the stuff they're doing elsewhere. The central section/step plane isn't changing, just the throat of the tunnels, and the edge wing is being raised, and stiffness tests on upward deflection. That means the edge wing will still bend down and act as a skirt.
The changes don't seem well thought out to me. Hopefully the changes are axed, those diffuser strakes will create more outwash lower in the diffuser, which is antithesis to the new regulations.
One thing I don't understand is why teams aren't taking advantage of the fin you can put in the middle of the diffuser under the crash structure.
Unless I'm reading the regulations wrong or this image is outdated, there's a lot of diffuser space that isn't being used for flow conditioning in the center.