Not all of the best by a long shot because of how many people (including "white" people) who never got a chance to develop their skills to that level, but yes, they of course were the best of the best.
They were because there are a heck of a lot of people who look vaguely like that. Unless you're embracing discredited ideas of racial superiority in something, meaning that the best of the best out of hundreds of millions of people--simply because structural factors (including outright bigotry) meant that they happened to be mostly-white, mostly-male, and mostly-not-poor--are actually kinda bad compared to some other exalted gifted group, then yes, they actually were very good at what they did.
Now, did they do everything? Of course not, not by a long shot, and anyway, culture and technology is constantly evolving giving more to do even if everything else is static. But to doubt that the best of the best are about as good as they come simply because of racial bigotry is, well, racially bigoted. They (mostly) deserve their accolades.
What is a tremendous shame is that so many people weren't given the opportunity to build their skill and deserve accolades of their own. Especially since in creative endeavors, diversity is unusually directly applicable. That doesn't take much away from the set who did, however.
It also doesn't mean that people are going to stop finding greens and blues more calming than reds. A lot of design reflects human nature, not culture, and we're hardly likely to find out what is what if we throw out all the hard-won knowledge that happened to be produced by groups of people with low levels of diversity in some aspects. Of course you want people eager to share the craft, as developed, with people who were formerly excluded! But you also want to probe the supposed knowledge to see what really holds in general, and what was so culturally specific that it doesn't even extend across the kinds of differences that one can find in design school.
If design wasn't always challenging its presumptions, it was missing out on opportunities to develop to begin with, identity-group-composition notwithstanding.