It is ok to build on somebody else's business IFF you have a contract in place protecting you. The problem is, today, there are few contracts signed because that would prevent tomorrow's pivot (that screws all of today's partners).
"Tomorrow's pivot" :) I think you summed up all of it with that phrase.
Your quote reminds me of Netflix too. Here we have public company built on someone else's "business" (as Hollywood calls it).