...I think they (Kalin and Jaren) saw the success that Zach had working with Beck and wanted to see if Jaren could have that same kind of growth and development.

Comparing Romney and Hall in 2019, Romney made quicker decisions and was more effective throwing short routes like screens and slants. He was very good at getting the ball out quickly and to his first option. he was also better at not taking sacks and avoiding pressure.
In limited reps, Hall was more dynamic throwing down the field. If you exclude throws behind the line of scrimmage, Hall was statistically better than Romney in 2019, he was more accurate throwing downfield and had fewer turnovers and turnover worthy plays on deep throws than Romney did.

I think if we saw anything with our offense last year is that we need a QB who can stretch the field consistently to keep defenses from stacking the box and crowding the short to medium routes.