The general difference between Ryzen and Intel is pretty overstated because of some initial issues at launch, but it's true that if you're looking to lock at 144 FPS, and don't have interest in the multithreaded capabilities, Intel i5 and i7 K SKU's will give a higher maximum/average framerate (although in many cases, it also has lower minimum framerates as well). That said, it's generally a difference of 125 FPS for Ryzen vs 140 FPS for Intel - at any resolution higher than 1080p, you're unlikely to ever be CPU limited on any contemporary AAA game that stresses the GPU at all, even with a 1080 Ti.
In theory, the 1600Xs are higher clocked, but in practicality, nobody has been able to find a meaningful binning difference between 1600 and 1600X - the X SKU's are largely for people who are solely interested in out-of-the-box performance, such as professional users who would be locked out of overclocking regardless.
Anyway, G-Sync probably wouldn't matter if you were locked at exactly 144 fps (improbable in any use case), but it's false to say the only impact at high fps is screen tearing. It's literally dynamically refreshing the frame draw, instead of being variable. Most use cases at 1440p will look something like this - lets call it a steady 100 fps on a monitor refreshing 144 hz:
7 ms
14 ms
7 ms
14 ms
7 ms
14 ms
7 ms
14 ms
You're flickering between 72 and 144 hz with every frame, it essence. The G-Sync will draw the frames smoothly:
10 ms
10 ms
10 ms
10 ms
10 ms
10 ms
So it's not just screen tearing - it's all the associated stutters that come from the frequency of the monitor not being synchronized with the frames being provided by the GPU.