I think you have to remember that there was a lot of gossip back then about how Corbett was an...I don't know how to say this in mixed company but...an expert "yodeler in the valley of life and death." If you catch what I'm saying. So, he was incredibly well-known to the ladies. That's certainly a type of fame. I would argue that puts him over the top here.
Jeffries because he was the undefeated undisputed champion recognized by the whole world. Corbett wasn't. The British world didn't consider him the champion. Boxing was naturally more popular in 1905 then 1895 anyway.
I don't think it really matters when it comes to comparing overall fame though, Jeffries wasn't all that popular when he was actually champ and was seen as underwhelming early in his reign due to struggling so much with Sharkey, Corbett as well as Fitz in the rematch. Corbett, on the other hand, beat the biggest cultural icon in sports at the time and sold out pretty much where-ever he went. IMO, Johnson winning the belt did Jeffries a lot of favours with regard to how relevant he was amongst the general public. Johnson's cockiness made the search for a Great White Hope more frantic and who better to be this WH than the champ who retired undefeated?