I think I completely agree with you accept for Intel being at the start of the slide. I think the real beginning of the end is when they abandoned work or any hope of creating mobile products. (phones not laptops). They botched the Atom stuff up terribly... granted in hind sight and ironicly enough Qualcomm may have used some Intel style tactics to ensure Intel never got a foot hold. Still Intel screwed that up themselves. They also sold off Xscale... they probably should have leaned into that and had their own ARM chips to sell. Qualcomm may have been playing dirty... still if Intel had been putting out a product that was better they would have wiggled their way in. Just even then they where not willing to push through the pain of a few quarters of bad numbers... and just sold xscale off instead.Not really. It will take a long time of serious decline before there are massive issues.
Almost all of OEM sales and server sales are dominated by Intel. If Intel suddenly ceased to exist then 'the world' would be in serious trouble as quite frankly AMD and other niche manufacturers wouldn't be able to supply the void that Intel would leave behind.
If AMD sells every chip they make or it's possible for them to make, Intel still would have a lion's share of the market.
However, piece by piece the money will start to go other directions. Fujitsu released one of the most powerful super computers all using ARM. Apple is moving to ARM (they're relatively small, but roughly 10-15% of the consumer space). And AMD is continuing to show their server and workstation chips are worthy of real consideration.
Much like IBM, Blackberry, Xerox, etc, it will still take likely 10 years for a full decline like that to happen. Intel should be concerned. They should fix their problems now. Otherwise they have nothing left other than a long slow death. But make no mistake: we're just at the beginning of said long slow death.
If we think about it the #1 personal computing market today is mobile. Android dominates and it all runs on ARM chips and not one of them is produced by Intel. Of course AMD isn't there either... but AMD is a much smaller company that wisely decided to focus on their core products. (they at one time had smaller mobile market aspirations as well) Intel could have owned that market... they where developing high performance mobile before the market really settled into the ARM/Android standard of today. If Intels leadership at that point... hadn't been thinking short term write offs they could easily today be producing the fastest ARM designs. (instead of Apple of all companies being the ARM core kings) They may have also been able to further develop Atom and at least keep the market spit up a bit.
As it is now ARM is monster.... not related but I have a feeling if Softbank does sell ARM the price tag is going to be something insane like 60-80 billion.
Intel tapping out of that market in my opinion was the beginning of their slide. Had they dug in with mini x86... or at least positioned themselves as the ultimate ARM design company. What a different place they would be in today. Right now they are getting destroyed in HPC by a ARM design (its not just one of the fastest super computers right now fugaku IS #1.... the planned new #1 Intel based super computers coming up don't have working chips yet) I posit that would not have been impossible if ARM hadn't grown off mobile. The next few years we are going to see a lot more ARM servers... I know its been hyped for ages, but its coming the code issues that have hampered every ARM server so far are being solved. (as fugaku helps demonstrate) Apple leaving x86 is going to have some serious consumer ripples... Intel may well loose a lot of the Laptop market that has been its consumer bread and butter. For sure they loose the 15% of so that was Apple sales... but all indications are Apple has the right chip design team in place to really shake things up. I wouldn't be shocked if Apple grows their laptop market share to 30-40% by 2024 if they price their ARM macbooks to grow share.
Anyway I don't mean to write a book... simply believe Intel has been on a slide for almost a decade now... I remember when IBM fell. It was gradual as you say. However there was also a solid decade where people of the day would have said IBM will never fall they are IBM. However in retrospect everyone knows the day they made their MS OS deal it was all over. IMO Intel signed their sunset papers the day they told investors... Xscale is a looser, and doubled down when they ended Atom development.