Hey buddy I posted about this:
It seems you are underestimating the PS4 Pro.
I don't mean to sound harsh (and I'd love for it to be true), but I think it's more likely that you aren't sensitive enough to the framerate to be aware of drops below 60. I'm partly basing this on the 1X version seeming to run between 40-55. In the sense that I don't doubt the Pro could run slightly better than that with lower settings, but the "lock" you're describing would be an anomaly.