Apple won't give control up and allow Vulkan support, so they really need to bridge the gap here by creating a solid player base to incentivize developers to natively support.
The first step to that is to take their gaming division seriously, something they've yet to do lol. These half-steps really don't move the needle.
It has nothing to do with control. Metal was first and Apple needed something more performant than OpenGL, Khronos Group dragged it’s feet, so Apple made what they needed. You can build Vulkan to iOS a number of ways.