PS my 2nd thought about this after coffee - and this would be my "advice" to younger self. You get a foot in an organisation by attention to detail, then you move on by cultivating bigger stuff. Obviously this colleague's eye for the "bigger stuff" is better than his attention to detail - so tell yourself this is a chance to study for yourself the bigger dynamics. That might just help you to step back from putting across an attitude of criticism. Say to your inner critic that you are now studying Human Relations, so quiet on the details.

Hope that helps. I'm a perfectionist at work because it's a habitual attempt to control and stay safe. But losing one client is less important than upsetting someone in your team in the long run, so check your internal turmoil before launching out. "only a website, not WW3!". Calm wins!