I have to very strongly disagree with this sentiment. I have personally tested quite a few no-name "4K 60fps" cameras from Amazon and AliExpress. Many of them upscale from 1080 - which is fine I guess - but then in 60fps will use a crop sensor and upscale from like ~640. Even with the more recognizable SJCam and Akaso brands, unless you're paying ~$200 - you're going to get upscaling, bad color science, bad image distortion. When comparing against a GoPro 5 (first 4k 60 entry) or 8 (first with USB C) the difference is astounding.
Though perhaps this is the difference between good and great that you refer to - but for me, it's certainly worth getting a used GoPro vs any of these modern cheap alternatives.
Unfortunately current new GoPros don't improve on their existing line enough to justify paying current prices. I wish I could get a new 2018 quality GoPro knockoff for <$200
ISTR GoPro moved away from Ambarella SoCs several years ago and rolled their own, but most of the other cameras are using Amba, Novatek, etc., and certainly offer great performance for a fraction of the cost of GoPro.
On a good camera the difference is stark.
However once it got a bit darker, or heavy movement, the big brands left the rest in the dust pretty much.
So yeah, do a bit of research and figure out your use-case.
What about equal-or-better-than-the-same-or-similar-GoPro?