Did you even watch the video? The Intel systems had problems and hitching. The only issue mentioned on the Ryzen was pop-in in GTA5 and that's not a CPU issue. It's also weird they mentioned the issue on Intel and then decided it's not big deal. Hitching is part of "smoothness". The second caveat is that 3 people is a small sample size. The amount of reviewers that have mentioned smoothness is greater than in this video.
Quotes referring to the intel systems.
"System 1 was noticeably bad. There was a lot of hanging up and it actually affected the gameplay."
"Minor? Ugh... would it stop me from playing GTA V? Probably not. But compared to the other systems, it was noticeably different."
And then the contradictory conclusion:
"It's as we expected, we were able to tell very little difference. The idea that these systems are noticeably better or smoother, was not really the case."
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Here is another instance you can clearly see the i7 is massively stuttering in gameplay.
The actual comparison starts @ 5:30.
Slow the video down to half speed, and go to @6:16. You can see the game hang for a considerable amount of time. That one image is just frozen on the screen.
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In this Hardware Unboxed video he noted Intel system periodically stutters, not only in GTA V, also in Watch Dogs 2 and BF1. Very smooth on Ryzen in these games.