Yeah, but that doesn't seem to have helped much to keep the Vulkan API small and tidy, instead there are dozens (or maybe hundreds by now?) of vendor-specific extensions.
I think this is vastly overstated. I've done quite a bit of work for Vulkan, and have done just fine without reaching for extensions.
And how else do you propose accessing hardware features which are vendor specific?
Doesn't khronos contain people from a bunch of different corps (amd, nvidia, intel, qualcom) for this exact reason.