Melanin, among other things, does appear to have positive influence on skin mechanical resistance.
There are some papers that try to take it on this hypothesis.
The theory is that paler skin tones evolved among populations that started to wear lots of clothing not only to allow more vitamin D3 synthesis due to UV radiation, but also because tougher skin wasn't that advantageous with lots of cloth cover.
https://www.ucsf.edu/news/2016/06/403401/darker-skin-stronger-skin-says-new-view-human-skin-color
https://www.mdpi.com/1996-1944/16/5/2023
https://www.mdpi.com/1422-0067/24/5/4360
It's probably strictly visual in many cases, though. Ngannou's face was pretty damn swollen after first Miocic figth, but it's not as easy to notice as very visible hematomas.