I think the vertical-oxer combination asks a very different question than the oxer-vertical. Personally, I don’t think that the number of strides between them actually is what makes the difference (just speaking from my own experience).
A vertical in with oxer out is asking both the horse and rider whether they can maintain focus on the first part of the combination until it is completed, then address the out. It’s very easy to have the vertical down because of already thinking about and preparing for the oxer. Whether it’s having it down in front because of thinking too early about needing additional impulsion for the out and adding power too early, or conversely, having it down behind because of needing to collect in that first stride and then be able to still have the impulsion to get out over the oxer.
An oxer in is, IMO (and depending on the horse, of course) much easier. When I was showing my little mare, an oxer in was basically a freebie combination - as long as we found the in, there was minimal participation on my part other than maintaining balance to get out. A vertical in required a more technical and thoughtful ride. Both of them ask very valid questions of horse and rider.
I certainly won’t pretend that I ride, or rode, anywhere near the level of Harry Charles. Nor will I ever. But this strikes me as an emotional reaction to an understandably frightening experience, rather than truly a global issue that requires intervention in course design.