Hi Marcus,
I removed the links you provided to a Japanese PC vendor. For the purposes of this discussion please feel free to discuss the system specs without linking to a vendor website. You can copy and paste information if you need to.
Regarding your question - both machines have benefits. Strictly speaking the i9-9900k might be a little more powerful, but they are roughly equivalent. The i9 has the same # of cores and roughly the same cache as he Ryzen, the same TDP, and the clock speeds are comparable.
The major benefit of the Ryzen is the extra RAM. If you're editing in 4K, it can really help. Premiere will gobble up whatever RAM you can throw at it, you will feel the difference while editing, especially if using multiple layers and effects, and your renders will probably get a noticeable speedup.
I worked professionally with Premiere/Final Cut/AVID machines for many years and honestly if I were you I'd probably go for the Ryzen. But, I think either of those computers you listed will suit you well for working with 4k footage.