It is illusory, because the player's ability hasn't changed, he's just getting more minutes. If you take Kobe Bryant today and reduce his minutes to 20 per game, guess what? His production will fall. Not because his ability changed, but because you can't accumulate as much production when you play less. The reverse is obviously true: if your ability doesn't change, but you get more minutes, your numbers will obviously rise. Numbers rising with minutes is not much of an indication of greater ability.
Coach trust is quite different from actual ability. If there was such a massive difference in ability, it would show itself in his per-minute efficiency. Maybe not perfectly, but to the extent of posting somewhat better numbers on a per-minute basis.
He played 8 games, which is a pretty meaningless sample. Of course, his rookie season doesn't help your point (I didn't exclude it to help my own point):
2003-04: 16.4
So, he actually "got worse" after his rookie year (of course, an 8 game sample has virtually no level of statistical confidence, which is exactly why I omitted it).
I am not really saying Outlaw hasn't improved at all. His defense has improved and his court awareness has improved. But those are things we can't really compare to Miles in this discussion because that would take a very close watching of Miles through his career that we probably don't have. Comparing their production, both have stagnated and there's very little evidence that Outlaw "worked really hard" while Miles didn't.