Both matter quite a bit. The first-mover advantage obviously rewards OEMs in a first-come, first-serve order, but CUDA itself isn't some light switch that OEMs can flick and get working overnight. Everyone would do it if it was easy, and even Google is struggling to find buy-in for their TPU pods and frameworks.
Short-term value has been dependent on how well Nvidia has responded to burgeoning demands. Long-term value is going to be predicated on the number of Nvidia alternatives that exist, and right now the number is still zero.
It's almost as if being a first-mover is more important than whether or not you use CUDA.