Before starting, AMD signed an agreement with Intel that gave them an explicit license to x86. And x86 was a whole lot smaller and simpler back then in 1982. A completely different and incomparable situation.
Technically it was after starting - AMD was founded in 1969 as a second-sourcer for Fairchild and National Semiconductor, and had reverse-engineered the 8080 by 1975 and acquired a formal license to it by 1976.
The 1982 deal you speak of was actually pretty interesting: as a condition of the x86's use in the IBM PC, IBM requested a second source for x86 chips. AMD was that source, and so they cross-licensed the x86 in 1982 to allow the IBM PC project to proceed forward. This makes the Intel/AMD deal even more important for both companies: the PC market would never have developed without the cross-licensing, which would've been bad for all companies involved. This gave Intel an ongoing stake in AMD's success at least until the PC market consolidated on the x86 standard.
Was there a large entity steering x86 spec alone with a huge feature lead against their competition, free to steer the spec in any ways they choose? Also, hardware is not opensource software, you get big players onboard and they will be able to implement the spec they want every gen, software has more moving parts and unaligned parties involved.
I had't considered that angle. Is your point that Intel was the creator of x86, but software chose to support it, then AMD had nothing else but to play catch up in x86 support to be part of the software target market? If so and factual (I've no idea), fair point, I didn't know.
And Intel named its licenced implementation of AMD64 as IA-32e, just to make it clear to everyone that it is based on Intel architecture 32bit version with an extension.
Luckily they dropped that name few years later
