Harden was ferocious taking it to the rack. At crunch time he was reliable.
I've long been a Harden advocate. When people were saying that his numbers were inflated by going against other bench players and playing alongside Durant and Westbrook, I argued that those players stifled Harden's production, as he's a player who flourishes with the ball in his hands, particularly in pick-and-roll. I was adamant about Harden being the best SG under 30 when people were comparing him to a litter of inefficient gunners and dime-a-dozen role players. I was convinced Harden would re-sign with OKC, in spite of the financial hurdles, because I believed he was too great to let go. My hard-on for Harden is well-documented.
With that said, there is no basis for your claim regarding Harden's reliability in crunch time, because he pretty much never had that opportunity, outside of Game 4 in Dallas. Harden's Game 4 performance against the Mavs was so remarkable partly because the Thunder relying on Harden to "ferociously" take it to the rack in crunch time was such an aberration. The only reliable thing about Harden in crunch time was that you could rely on him not getting the ball.
Here is James Harden's shot chart for clutch situations (last 5 minutes, margin of 5 points or less) for the entire 2011-12 regular season:
That's 3-11 from the field in 132 minutes (he was also 14-19 from the FT line). He had a miniscule usage rate of 6.5% in those situations (compared to 21.6% overall).
Kevin Martin is 7-11 from the field in 89 clutch minutes this season (4-4 from the FT line), with a 6.9% usage rate.
Here are Durant and Westbrook's clutch stats from last season for comparison:
Durant - 151 minutes, 47-119 FG, 37-42 FT, 41.4% usage rate (31.8% overall)
Westbrook - 151 minutes, 37-88 FG, 46-50 FT, 37.2% usage rate (32.0% overall)
In other words, Durant and Westbrook dominated the ball in the closing minutes of close games even when the Thunder had Harden. The only thing that has changed is that Durant's usage has gone up a few points while Westbrook's has dropped a few, but their combined usage is nearly identical (it's actually a 1.2% lower this season).
Martin does pretty much the same thing Harden was asked to do in crunch time: stand behind the 3-point line while Durant and Westbrook work for shots.