It is a bit of a conundrum that we encourage the use of primary sources where we can find them but are happy to rely on secondary, or even as you say, tertiary sources for notables.
It is true that often the articles you can easily find for notables from the last 500 years or so, such as in Wikipedia, are often reasonably correct and well researched. Though as someone pointed out in a G2G question recently Wikipedia doesn't encourage the use of primary sources.
Personally I think the priority is on those profiles that don't have any sources or dubious sources, but I don't think it hurts to add interesting information such as details from the 1881 census or other primary sources we come across to notable profiles.
If eventually the profiles on WikiTree for Queen Victoria or Empress Eugenie consist mostly of primary sources that confirm details about their personal life, and we link to Wikipedia or elsewhere for aspects of their history then I think that would be very useful.