There are three things going on here.
1) The Pro has two SKUs while the XB1X only has one. Here are the Pro SKUs along with their position in the current best sellers list
(not 2017 list).
- #62: PlayStation 4 Pro 1TB Console
- #132: PlayStation 4 Pro 1TB Console - Destiny 2 Bundle
2) There is a larger power differentiation between the base XB1 and XB1x giving a greater motivating to upgrade. The XB1S is still going to be the largest seller of the two, but the XB1X could end up getting a higher percent of the platform sales than the PS4 Pro.
3) The XB1X is getting a boost due to it launching this year. All the enthusiast early adopters are queuing up to preorder vs the PS4 Pro early adopters buying last holiday season. The Pro and the XB1X are premium products specifically targeted towards the enthusiast market, thus both should have sales more front loaded than normal.
As with the release PS4 and XB1, we'll have to wait until the early adopters have been satiated before we can find the base demand. Remember the XB1 hung in there with the PS4 during that first year
(although XB1 dropping the Kinect dead weight had a lot to do with that).