A practical generic solution, for example, that takes an extra 10 days to do, sounds fantastic from an engineering perspective-- we're trained to think this way. But on the business side of things, you may have a timeline for a feature to nab a client, or not enough budget for those extra 10 days, etc.
My opinion on these matters now generally falls into the it depends camp. Take his mentorship, because it sounds like he understands that every engineering solution is accompanied by a business solution and they must be agreeable for both parties (that said, he does seem a little jaded, so you don't have to take absolutely everything he says to heart-- there are companies who will give less weight to the business side of things, but the reality is that the consideration will always exist).