At this distance, the only info on the parish registers will be the names, unless you’re lucky enough to find a marriage register which states that one of the wedding party was from elsewhere, or was married with the consent of a named father. Records are patchy and not very legible when you go that far back, and I think it’s perfectly possible for someone to find that there’s only one person listed with the correct name, and assume that that is them. Of course there may have been several others, but those records haven’t survived.
Having said that, I can’t see a baptism in Ullesthorpe for someone of this name in 1590. The closest I’m getting is 1587 in Bitteswell, or 1600 in Countesthorpe. FindMyPast isn’t giving any BMDs at Ullesthorpe for anyone called Sut*n in this time period. (Added - in fact FindMyPast doesn’t seem to have any PRs at all for Ullesthorpe until the 1800s, so I wonder where the ancestry tree owners got their suggestion).
Have you tried looking for wills, court cases, tax details etc to see if you can uncover anything else?