Prime isn’t the question. Does that also account for being serviceable player?
There is more to learn being a defenseman than a winger because of the added responsibilities and impact of a mistake can make when you are playing the position closest to your own goal.
I didn't just say prime. Prime is the same. The tail off after prime is the same. The pre-prime ramping up is the same. ALL evidence points out to them being the same.
There is no evidence that they are not.
Now, the absence of evidence isn't evidence of absence... BUT there is evidence for one, and not for the other.
Also, no. There's not more. It's just mistakes end up being more high leverage so it registers more in the mind, thus causing you to be more conservative with taking chances on players. The impact of a mistake makes coaches and GMs overly cautious to a fault and trust the devil they know, which causes a later entry into NHL on average, but the actual developmental curve in performance is equatable.
Part of the issue is that the market is just worse at evaluating defense (the impact not the position) than offense. This makes sense. The eye test relies on events and actions to evaluate ability. Defense is primarily the absence of events, something the eye test is weaker at. Defenders (position) tend to have a higher percentage of their value driven via defensive impact than forwards. This is why we see stats like GAR/60 correlate higher to TOI/GP for forwards than defenders.
!!! In fact !!! I'd argue that the fact that there is a lot more poor evaluation in defenders, until the market adjusts, it's actually earlier for defenders to be "good enough" to get in on average than forwards... once the market adjusts though you'd likely get similar entry.