Vulkan is almost 1:1 equivalent to "modern" OpenGL except the need for a more advanced allocator. You had to write the exact same thing in OpenGL if you wanted decent performance, except through an entire translation layer.
I don't think anyone who actually worked on a serious engine thinks it's somehow harder to use. Sure, there's more boilerplate and it might get pretty difficult to port something to it, but that's something else entirely.
Except one also gets to compare Vulkan with Metal, DX 12, LibGNMX, LibGNM , NVN, all of them with a bit more developer friendliness and tooling in mind.
Which I guess, it is where the resistance is coming from, hence the need for such presentation.
I don't think anyone who actually worked on a serious engine thinks it's somehow harder to use. Sure, there's more boilerplate and it might get pretty difficult to port something to it, but that's something else entirely.