So Intel goes cap-in-hand to AMD for their tech.
Intel isn't threatened by ARM yet in a performance laptop.
Of course one could reply laptops don't need that much power anymore to do what most users use them for today (thus people even here using tablet as their main tool) but that's another issue entirely, "much cheaper and good enough", one where Apple isn't Intel's main opponent either (I would even wager in that one, Intel is its own ennemy, given how terrible they've been handling the Atom brand and performance to protect margins).
Not sure I get you re Apple being an opponent to Intel for "cheap" parts. It goes without saying that Apple would not sell their own stuff to anyone else. And for their own use, I'm sure the hardware would be very cheap to manufacture.
Intel has to worry about Nvidia taking over the graphics and machine learning, AMD punching above its weight in workstation with EPYC and ThreadRipper, and ARM being cheap and good enough in all the low power fields and growing.
A middle of the line, ARM based performance oriented chip for laptop is no threat to i5/i7, except indeed the risk to lose their place in macs.
If they ditched Intel, that would very publically rip a stripe off of Intel, regardless of absolute market share. Not something Intel wants, and is what I contended Intel have gone to an unusual length, integrating AMD graphics, to avoid.
Now they should co-develop and promote a well designed open source ML framework, something that can compete with CUDA. AMD isn't up to the task, but Intel is.