It seem that skull walls and purple walls not really much difference in war ranking weight but defenses are.
But for th9, weight of level 10 walls weight really ridiculous. I was once with 70 percent lava walls the rest lego walls with level 2 both xbow, all level 10 archer tower but one level 9, all mortar still level 6, all cannons still level 10 and overall heroes level 42 ranked higher than a maxed defenses th9 with half skull, half lego walls with overall heroes level 20, at that time.
But in your case, still hard to comprehend given your overall defense looks better than him.

