Anyone who was actually paying attention realized Arch was overrated by his senior year in high school. He was a top-ish QB for the class on a par with the others. None who have set the world on fire either.
Julian Saylin (his opposite today) was similarly overrated during his junior year, but not being a Manning fell down the ranking a little (still, he is the starting QB for Ohio State). You will note that Saylin didn't exactly set the world on fire today either.
The Texas offense will gain some momentum against weaker teams and Arch will grow in confidence. Opening up the offense a bit will open up running lanes allowing him to be good college QB by midiseason (that and having NFL talent all around him, which never hurts).
Give the kid a bit of a break. This isn't a reprise of the Sanders hype where the kid ate it up and believed it. The Manning family has been trying to downplay things from day one (perhaps over doing it, if anything).