He's not just the 15th most efficient player on offense -- PRPG! is an attempt, as flawed as such things can be, to make a comprehensive "points above replacement" metric similar to WAR in baseball only for college basketball. That includes production on the defensive end, such as rebounding or blocked shots, not just scoring.
Bolton is roughly the 15th best player in the conference not just on offense. If we were to take Born and redshirt him, he would be quite the developmental success story if he becomes as good as Bolton is now by the time he was a fifth-year senior.
I would argue that Wigginton had some higher highs but also some lower lows. Wigginton went off a few times, but there were games he basically lost on his own, too, bricking shots and trying to force drives that were not really there.
Bolton is not quite as good of a shooter (though he has been much better in 2020 than in 2019) and is probably a better finisher/better at drawing fouls. Either way, these are relatively small differences. Their physical profile, style, play, efficiencies, and advance stats are all very similar to each other. Bolton replaced Wigginton in as close to a 1-to-1 fashion as you basically can at this level. Things might be pretty ugly (e.g., 0-10) without him.
What we did not replace was Horton-Tucker.