A good VO2 max capability is definitely important to good performance.
OK, so its not the most important factor - that one goes to whitewater gate skills. But at a high competitive level, all aspects of physical ability need to be worked on. Slalom is a middle distance sport - a good mix of anaerobic and aerobic abilities is required, with repeated single stroke efforts at high power.
I never think of testing as a comparison against other athletes, only against myself.... has my power improved since this time last year? Has my VO2max improved in the last 3 months of specific training? I will never have the max power capabilities or the absolute VO2max of bigger guys like Huw Swetnam, so I don't pay too much attention to those kind of comparisons. If you want to compare against others, it is better to compare results relative to bodyweight. This is more relevant to slalom where we constantly change direction and re-accelerate.
[You need to note that VO2max can be quoted as absolute, in units of litres, or relative, in units per kg bodyweight. Simply saying someone has a higher VO2 can be misleading if you don't quote the units too!]
Think of this.... if I had the same skill, power etc etc, yet higher VO2max abilities....
I would be able to sustain a high pace for longer in a race run
OR
hold the same pace as before, but have more energy in reserve towards the end of a run to minimise technical errors and maximise on opportunities to gain time.
On either account, the chances are that I would be a little faster.
I'd love to be a little faster!