While I definitely think you could make a case for Matas being better as a prospect, there is a pretty wide gap between the the statements "You could make a reasonable case for Matas" and "Matas is significantly better".
FWIW, your sample size is also a small segment of the season and Matas was well above his season average in that segment and Franz was well below, so a bit unfair to then say if you look at Matas's best part of his season and Franz's worst, then they were similar.
Either way, after their rookie years, I would probably have leaned Franz, but I can definitely see the case for Matas. Mixing in what we know about Franz today (that the shot never came around), I'd probably take Matas's upside of putting it all together.