Tommy Rees only knows about what Brian Kelly allowed him to run. While that may not have been too much of an issue with a well-seasoned quarterback at the helm the likes of Ian Book (and to be fair, we could run most of the playbook with him, just not the long range game) who has a shrewd mind for being able to make adjustments on the fly, that was sufficient for getting us to that top 10 level.
However, when he doesn't have Brian Kelly to dictate to him what he should run, he seems to hide in his shell, and enter "WWBKD" mode. This was painfully obvious when he wouldn't call a simple quarterback sneak on 4th and 1 with a strong quarterback and all-American Jarrett Patterson on the line. That, plus he kept making last second play changes with only 8 seconds left on the play clock, because he got cold feet. As that play clock gets down closer to zero, the defense gains more of an advantage on being able to jump the snap count.
Charlie Weis Jr., on the other hand, has plenty of experience with multiple offenses. I'm pretty sure he has a very good grasp of the Erhardt-Perkins pro-style offense, since that's what Charlie Sr. ran, and I'm sure he's watched every tape of Tom Brady he could find. That, plus he understands blending in the spread offense with various other schemes, such as the veer, run-heavy pro-style, and even parts of the Air Raid offense.
I know some people will say "hey, look at Tommy Rees' record as OC from 2019-2021" and again, I don't dispute the fact that we had three 10 win seasons, and two top 10 finishes. However, it's becoming much more evident to me that Brian Kelly continued to call the plays, or at least give Rees a list of pre-approved ones.
That being said, at this point, I'd much rather wait to see what Charlie Weis Jr. can do at this level in the SEC, before making any more judgements on him. It's too early for him to be a full fledged OC at Notre Dame, just as it was way too early for Tommy Rees to be one.