Interesting but strange subject this one, of course Spider-Man was co-created by Lee and Ditko. In fairness Ditko also had trouble to keep the webbing on his costume consistent. In practically every panel there was a mistake with the webbing going the opposite way on the left and right gloves and boots. Compare both of his gloves on the cover of ASM #2 the first one of Ditko, the webs are in opposite directions. This problem continues throughout the issue. Likewise for issue #3. There's even a full-page pinup in that issue where Ditko gets it wrong on the gloves again. Also, Spider-Man's "belt" has either one or two horizontal weblines depending on the panel. Maybe this goes on all the way to his last issue but I don't have all day : )
So the inability to keep the webs consistent is not a good argument against Kirby but I think Kirby was just not expressing himself properly about creating the costume.