It's possible to improve the winevulkan thunks a bit, to mend the gap between the current direct calls and the new path. It's still not going to be anywhere close to unix native performance but I think it makes the change acceptable.
Sure, if the dispatcher path would be very close in performance to the current direct call path, then there would be nothing speaking against removing the direct calls, but at least according to my testing with vkoverhead, that doesn't seem to be the case, even with the recent improvements.
I saw that Proton Experimental already pulled in the patch to use direct calls for vkGetDescriptorEXT, so maybe it is already planned to sick to direct calls there for a while longer. Regardless, I will try to patch the recent dispatcher improvements into Proton Experimental and compare the performance of some actual games with direct calls vs dispatcher in the next few days. Thanks for the response.