Based on s&p+ passing defense ratings of opponents ( which is an adjusted number Accounting for SOS).
Utah opponents are rated 101.87 on average, with an average rank of 68.58.
BYU opponents ( without Wagner, which isn't rated) are rated 105.98 on average, average rank of 51.45.
The Wagner game accounts for three TDs and 286 yards, so not much impact to leave it out.
In other words, SOS in terms of passing D has nothing to do with Tanner's excellent numbers compared to Wilson's