"So where you can do the same thing in two places, get the vendors involved and make sure you go for the best combination of options" . . . "Your particular combination of systems will almost certainly have unique interactions that the vendors’ specialists can help you with."
Good article, but you forgot a step (as many do): be large enough and buy enough kit that the "Vendors' specialists" deign to even recognise you as a valued customer.
"At the very least . . . you need to have the infrastructure team under one roof, preferably headed by a single manager."
Again, great idea but missing a step: have a CIO/CTO who understands the importance and benefits of such an approach and is able to manage the egos of said 'key service owners'. Also, along the same lines: make sure the CIO/CTO has hired people who are more interested in systems that work (and work well) than in protecting their own interests.
You are correct of course - the only way to get complex, inter-related systems to function together (let alone efficiently or, saints preserve, optimally) is to have the complex, inter-related employees controlling those systems also function together.
Unfortunately, working in such environments (at any level) is a rarity.