I have shot with L glass but never bought any lenses because my third party 2.8´s deliver good results. Shooting a 17-35 (performs well on a 5d3, tried it), 28-75 and a sigma 70-200 (good copy).
I´m also in europe and our canon service is slow, even more slow as i am in austria and many lenses and bodyie have to get sent to germany.
Yeah, weakest link in the chain etc. i know that. I didnt mean that good glass is overrated in general but with every new body everybody says you need the best glass. Thats true! But also the best glass from some time ago is still good enough.