OEM versions or 'made for' shafts are different, but that doesn't make them less quality. It just means the specs will fit a larger audience so to speak. This is what Preston Fugate told me when he was with Graphite Design. Last I saw he was with Puma / Cobra.
For example, an original / after market may have less torque, have a stiffer profile etc.. The Made For may have a mid torque and play more flexible than the original. Less torque and a stiffer profile doesn't make a shaft better quality, it just makes the specs fit a smaller number of golfers.
You could have the best quality shaft available, but if it doesn't work for your swing what good is it? Again, different doesn't necessarily mean less quality. OEM club manufacturers work with the shaft companies to get a shaft that works well with the club head for their intended customer. That generally means a wider group of golfers.
The majority of golfers swing less than 100 mph (most of them under 90 mph), so a made for shaft will work for most of those golfers. However, sometimes golfers want something different and may want to go the after market route.
It's all personal preference.