Be aware that if you switch to 60 FPS, the apparent resolution seems to drop. It seems like either it's not using the full resolution of the sensor in this mode, or the bit-rate is too low. Here are a couple of videos which illustrate the problem...
Did you try it with a scene with lots of detail in? And did you check the results on your PC? The difference isn't really noticeable when reviewing on the phone itself.
I've been amazed with the camera on my Pixel 2 XL so far, but I recently tried switching the video frame rate from 30fps to 60fps and couldn't believe how much poorer it looks! There's so much missing detail and the resolution appears lower. It seems like either it's not using the full...