problem is simple -- the entire existence of a gl is BASED on willpower. willpower is constantly mentioned, any feat they do willpower is exemplified.
because it is so showcased, it seemingly makes it very difficult to compare willpowers of other characters to willpowers of gl's. gl's have a tool to manifest willpower and make it clear how much willpower is being wielded.
wolverine -- or any other character -- HAS no such tool. does NOT being a gl automatically imply that someone's willpower<gl? what about deathstroke?
i'm not prepared to say wolverine's will>kyle's. i AM saying logan does not have the tool necessary to DEMONSTRATE the strength of his will as kyle does, thus making it almost impossible to 'prove' logan's will is equal to kyle's or ANY gl. does this mean ALL gl's willpower>logan's . . .?
that said, i DO think this is closer than many seem to.