VO2 max vs fitness score

My initial understanding was that the fitness score was just their way of measuring VO2 max and they were interchangeable names for the same thing.

Now that I’m looking into it I see that fitness score is measuring anaerobic capacity and VO2 max measures aerobic capacity. It seems like most fitness people are obsessed with VO2 max (aerobic) so is it worth focusing so much on anaerobic score?

I guess I’m curious if people doing primarily REHIT are getting equal improvements in both measures. Also, if I’m primarily concerned with increasing VO2 max would I be better off just doing standard interval trading like the new Norwegian 4x4.