Not elite like the D this year, but well above average. O has been winning games for BYU over the last several years. The O has generally performed better than the D for the last several years before this year. Pick basically any overall offensive statistic adjusted for difficulty of schedule and BYU O is above average to way above average. 3rd down conversion is not an overall statistic - total 1st downs is an overall offensive statistic and BYU is way above average for 1st downs.
Also, Jake is way above average for QB. The experts in the Big12, the Head Coaches, voted Jake 3rd best QB in the Big12. Sanders 1st Team, ASU 2nd Team and Jake the only Honorable Mention in the Big12 as voted by Big12 Head Coaches - those that would know. As you mentioned, Alex Smith was a great QB, but that was the exception at Utah. The last 3 QBs from BYU are on NFL payrolls. 2 have starts in the NFL. Not comparable to Utah at all. Utah has almost never had an O better than the D. BYU has recently almost always had an O better than the D. This year as an exception the O is good, but the D is elite. Again not comparable to Utah.
This is why, in only the 2nd year as a P4 BYU finished with a better record than Utah has ever had as a P4/P5. Not comparable. Hoping/ expecting similar to better performance next year by BYU. Go Cougars!