I'm pretty sure the point is more that - had Weave used a standard and already-vetted encryption method instead of rolling their own crypto - they could have put that free time into more useful things instead of now having to maintain yet another crypto implementation on top of their main project.

This isn't to say that there's never room for improvement in the crypto space - I personally disagree with the assertion that rolling one's own crypto is inherently bad in all cases, and instead believe that we need a maximum of innovation attempts now so that they can be evaluated and audited and identified as useful - but unless you're actually fixing a problem, Not-Invented-Here syndrome is dangerous and a waste of time better spent elsewhere.