Like a lumber mill that buys logs from a logging company? Who subcontracts to individual fallers? Who buy their chainsaws from a chainsaw company, their fuel from a petrochemical company? No business isn't entirely dependent on third parties. That's what it means to exist in a healthy economy.
A "farm-to-table" megacorp that owns everything from the source of every raw material through to the finished product is a nightmare, an entity that needs to be reigned in and broken up. Capitalism is a competitive game, but a game that can never be allowed to end.
This isn't new though. A ton of software companies are already completely dependent on AWS or Azure or whatever.
All businesses are reliant on multiple third parties doing their thing in order for the business to be viable. A lot of companies exist at the whims of Amazon or Walmart.
Go nuts with it, but we're at the SciFi dystopia test with: how do mega corporations even form? Well, this is certainly the plausible reality, they just start aggregating random income streams because their product is essentially the only thing that makes the business profitable. Without it, it can't compete.
Hopefully this sounds skeptical, but I don't see how you can have an independent business and be entirely dependent on third party for your operations.