Because given his criteria of "I have a PS4", it absolutely is.
Nope.
PC to Pro would be a massive downgrade,
He's already gone from PC to PS4. So apparently he's fine with the potential downgrade, which will be far less with the Pro (and debatable at all on a technical level with some multiplatform titles with a Pro patch - it's a 970, not a 1070).
why not keep the PS4 and PC and have the best of both worlds or simply get rid of the PS4 for a Pro?
Selling his PS4 will likely get him to just over half the cost of the Pro, so it's not a simple swap. And as he's said, he wants to get a laptop, primarily for classes, which makes far more sense than a desktop.
He can take the money he gets from the sale now before it depreciates further, get a more suitable PC platform for his needs, and a superior version of the gaming platform he actually uses.
You're missing out on a shit ton of amazing games if you restrict yourself to only being with Sony.
...assuming:
1. These games won't play decently on his eventual laptop purchase.
2. He actually has time for these games outside of the multiplatform titles, multiplayer and PS4 exclusives.
There are likely a fair number of WiiU and Xbone games I would get enjoyment out of, but like everyone I factor in the cost and time expenditure I would need to potentially enjoy them. If it were a simple matter of being 'restricted' by one or two platforms, then the only 'logical' choice would be to purchase every possible gaming platform.