I don't disagree, but when I look closely, I'm not so sure their formula is off by too much.
SP'ers are very important when they give 150+ IP, and although late innings are often higher leverage and of more importance, often times early inning situations are very important, too.
So many later inning games are more or elss out of reach, too.
No doubt, traditional closers are used almost exclusively in very high leverage situations, and just about every IP is of high value, but it usually is 40-55 innings like that.
I think SP'ers might pitch 100 innings of low to mid leverage situations, by they also have plenty of high leverage situations where a game can be won or lost early.
It's hard to know just how far they are off in their WAR calculations. It seems like closers do get short-changed, while maybe the rest of RP'ers seem pretty close to accurate, so I guess I am mostly agreeing with you.