L lenses were made far before crop sensors were made. Back when (canon) dslrs were all 35mm format. So yes, L lenses are 'optimized' for that format. Why do you think the image circle covers the full frame sensor? I don't think they were designing L lenses thinking 'You know what, in the future we're gonna make sensors 1.6 times smaller, so lets optimize our lenses for those in the future.' It was just by coincidence that aps-c gets the sweet spot. Ef-S lenses can offer superior IQ but thats because most are current designs (although some L's are getting upgraded). If you own a crop sensor camera and all you care about is IQ, L lenses are not for you.