I'm a little confused by what you're asking.

Do you mean how many adventurers in canon are as accomplished as our characters are portrayed? I don't think any specific characters are equal to us, but I think the game leaves the possibility that there are unnamed adventurers that match us. After all The Warriors of Light from 1.0 are officially part of lore and our character is portrayed as taking on some of the more difficult tasks with teams of other adventurers.

Or are you asking how many other adventures out there match us in-game? In which case I would say a probably a good couple hundred thousand :P Since there are probably that many people taking on tough content at level 50.

Or do you mean how many other adventures match us in our own RP-stories? If so the answers will vary from person to person Sadly, I haven't RPed in FFXIV so I don't have an answer for this one.