What you're not considering is the R&D costs of a node. Those are fixed, irrespective of how many customers or production volume you have. So, the more you can scale your production volume, the more you can amortize those up-front costs.
You're also assuming there are no economies to be gained by scaling up production further, which I think is also incorrect.
By your logic, IDM 2.0 makes no sense. Why would Intel have tried IDM twice, if it didn't make any sense, with even the new CEO talking up the IDM strategy in his first public announcements? Do you really think Intel is so clueless? And if IDM weren't essential to the business strategy, why wouldn't that have been tossed out, already?
You can't explain what Intel is doing (ignoring the current rumor), unless what I'm saying is right.