I get your point, but my problem with that line of thinking is that all of the people on the bottom half of that list are considered overpaid. Batum fits in right between the two groups. And really, SF is regarded as one of the easiest, if not the easiest, positions to fill in the NBA. So, unless you've got one of the difference makers at the very top of the list, it doesn't make much sense to pay someone like a franchise player when you could get more impact for your dollars elsewhere (small market issues aside).
As I posted here, Nic was 48th in the league in scoring last year and is the 49th highest paid player in the league this season. So, even with last year's 13.9ppg scoring average, Nic's salary this season is in line with his scoring ability - even if he doesn't improve his scoring over the 4-year life of his contract.
But, he has improved (so far, yeah I know it's only 6 games). Right now, Nic is 15th in the entire league in scoring per game, 4th in steals, 23rd in PER, 16th in EFF, 19th in WS, etc. Basically, he's currently performing like a top 20 player in the league, but being paid like the 49th best player in the league.
And, because Minnesota's front loaded his offer sheet, this year's salary is highest of his 4-year contract. Not only is Nic earning that contract (through 6 games), but he's looking like a bargain (so far). And, he's only 23 and still has room for further improvement - as his salary goes DOWN.
He may never be a 1st, 2nd or even 3rd scoring option on a contending team, but given his versatility and the other ways he contributes, that's actually a good thing. Now that he can score of the dribble, and is no longer just a spot up shooter, he can create for himself, and others, when teams double Lillard and force the ball out of his hands.
Is he the best small forward in the game? If you consider any, or all, of LeBron, Carmelo and Durant small forwards, then Batum isn't even in the conversation. But, even if he's only the 4th best SF in the league, behind those three, he's still a pretty damn good player, not overpaid at all (based on current production), young and still improving.
BNM