I wonder if you actually believe what you are saying or are trolling?
There are significantly more than 2 companies that can make x86 chips, fyi.
It is impossible for anyone today to license the x86 ISA and design a new CPU with it, not only for legal reasons, but also technical reasons. Basically it is too complex to do it from scratch without infringing Intel patents and burning an insane amount of money, as Intel or AMD will not help you in any way to get it right.
Intel has killed all the competition with a combination of successful engineering and dubious business practices (what weight you give to each is a very personal view), so that means that nowadays the situation is that if you need x86, you need Intel.
And the variety of ARM chips, at least outside of the low end embedded market isn't that great. In fact, the vast majority of them are almost completely the same, they are basically taking the ARM kits and fabing them.
The increasing number of ARM licensees, both architectural and for ARM cores, says otherwise.
you can't seriously say x86 is more "open" than ARM. although I agree saying ARM is "open" may not be accurate either.
The fact that ARM is the only one defining the ISA is not even true, the ISA itself (actually the architecture, it is more than just an ISA) is a product they sell, they take input from their customers about it.
They also sell tools to make it possible to design a CPU from scratch and validate it.
It is true that you can't design an ARM core and add extensions to the ISA, so in that respect the x86 ISA is more "open", but I think the correct word for it is fragmented.
And although this has happened in the past, in the current situation only extensions done by Intel will ever get some adoption, meaning it is the de-facto standard, not much openness about it.