I think it does matter to some people, but I don't think it's really that big of a factor in general. Both Izzy and Usman have plenty of reasons to be disliked, that don't involve their skin color.
I don't know you personally, but in general people who have made similar statements on here have seemed very biased in their view and seemed to be looking to confirm that bias. Silva has, IMO, the most delusional fanbase here on SD and that's all due to the love they have for him. Rampage was very popular too and even Jon Jones despite all the fuck ups still has a good amount of fans. DC is generally loved too. Of course you can find haters for all of those, but so you can with every single fighter, regardless of race. Oh and Reem seems to be pretty much universally loved on here nowadays too. Yoel is very popular too.