In terms of outrageous passing numbers they are both high up.
Leinart is doing shit because he is hurt and on a shit team. Bush is now injured but he was never a RB to pound the ball in between the tackles so I don't know why anyone is surprised he isn't now.
Cap if you look at the numbers, there is no comparison. In addition to what I said earlier about completion percentage, etc., here are some other numbers:
Chang
2436 attempts, 17,072 yards, 117 TDs, 80 INTs, 6 rushing TDs
Brennan
1546 attempts, 14,024, 131 TDs, 39 INTs, 15 rushing TDs
Brennan has 14 more TDs on 890
fewer attempts. He has 41
fewer INTs. He has 9 more rushing TDs.
I don't think anyone can objectively look at the numbers and say they are comparable. Brennan is head and shoulders better.
I watched almost every game Chang played and UH and I've seen every snap Brennan has taken. They are not the same at all. Chang had a stronger arm and quicker release (the quickest release I've ever seen other than Marino), but his footwork was sloppy and he too often made poor decisions, which is why he had 80 INTs. Chang was good and he improved a lot his last year, but he couldn't carry Colt's jock (and I like Timmy).
Brennan is probably the most accurate passer in college football history.