I think it makes perfect sense. The original xbox one is draftily under powered, while the regular ps4 is powerful enough. There really isnt any need for ,much of the ps4 fanbase to upgrade to the ps4 pro. While most gamers right now are on 1080p tvs ps4 can handle that. while just to get to 1080p on most games for the xbox one you would need an X. Ps4 Pro is just there if you want it. you dont really need it, because the ps4 itself is good enough.
I don't think that theory makes as much sense as it may seem at first glance. Let's first account for brand fans on both platforms who are upgrading just because they're loyal customers, and they also want to have the best Xbox or the best PlayStation (so not really because they're experiencing inadequate performance or anything like that). Should there be more such people on Xbox? I don't see why, especially since there are more PS4 consoles out there, and the upgrade to the X is $100 more expensive than the upgrade to the Pro.
Then people who have made the jump to 4K, and are looking for the machine to showcase their new TV. Should there be more such people among those upgrading to Xbox One X from Xbox One (S) than those who are upgrading to Pro from their base PS4? Again I see no reason why that should be the case. The jump is once again more expensive for Xbox owners, there are less of them out there, and Xbox One S already has an UHD Blu-ray drive.
So let's finally consider the scenario you're proposing, Xbox One (S) owners who are upgrading to the X because they're dissatisfied with the machine's performance, and brand loyalty is just a secondary or even non-existing factor. If people are fed up with 900p or worse games on Xbox One (S), would it not be cheaper for them to upgrade to PS4 Slim or Pro? They'd also get the benefit of gaining access to PS4 exclusives that they can't play now, and still couldn't if they upgraded to the X. Most Microsoft's big games are already pretty good on the base hardware anyway (the biggest franchises are running at either native or dynamic 1080p), so they'd primarily be upgrading for multiplatform releases - something they can also get on PlayStation, alongside the PlayStation exclusives.
Nah, I think the biggest factors lie elsewhere. People who really appreciate having the best console hardware have probably not had Xbox Ones until now, they had PS4s. Now that Xbox One X has the best console hardware, they might be compelled to get it over the Pro. Those who are looking for a cheaper alternative to a decent gaming PC might also be willing to pay slightly more to get the best console hardware.
Those who are just looking to get the second or third console are probably more or less equally distributed. Xbox One owners who are getting the Pro as their secondary system have to pay less than the opposite group, and PS4 exclusives are very compelling. On the other hand, PS4 owners who are upgrading to the X have to pay more, but there are already more PS4 owners out there, and the BC program, Game Pass, UHD Blu-ray support, and the best (and most silent) hardware could all be pretty attractive to that group.
TL;DR - I don't think that logic really supports the notion that there are more Xbox One (S) owners upgrading to Xbox One X than there are PS4 owners upgrading to PS4 Pro. At the same time, I think that there's a good chance that there are more PS4 owners upgrading to Xbox One X, than there are Xbox One (S) owners upgrading to PS4 Pro.