There's nothing wrong with the stock cooler per say; they are intended to cool a stock running system and keep it at reasonable temperatures. Some people over cool there systems for no good reason other than some preceived improvement that the componets don't care about 😉
One area where the stock cooler falls down is in terms of noise. I replaced my 3200+ cooler with a Zalman 7000 series, and later an XP-120, and both of these aftermarket coolers are significantly quieter than stock. That's where the benifit really lies in my opinon.
Ed