Cheap ARM servers using chiplets is an absolute nightmare for both Intel and AMD, because they might be willing to forgo single thread (which is vital to client workloads) to get max MT/mm2/W.
I am not sure its that big of an issue and will affect Intel waaaay more than it does AMD.
Designing and producing a CPU is pretty damn expensive. If you aren't Apple/Samsung/Microsoft/Amazon/Tesla(well for different reasons). Designing an in house CPU and converting your tool chain to is an incredibly long winded, expensive, and dangerous solution. Even when getting others off the market CPU, the whole infrastructure move is expensive enough. There was a really good reason not tied just to the fact Mercer was sooooooo slow that people abandoned Itanium near instantly when AMD created X86-64. As long as you have lets say an AMD x86 solution that's within 20% of the performance and still cheap, they would be much more likely to move to that solution. Just look at AMD they might have been 6 years too early, but they bought a Arm server company and just found the sales market of the device less than good.
Amazon isn't really going to sell them. Not without them basically offering a full tool chain for the companies they are selling to, that match up perfectly and it will always be realitively small companies. What this does mean is as a major ODM buyer (remember they were buying SL-SP almost a year before it was available). They have the funding to get a CPU design, negotiate with TMSC, and develop the tools sets (since they have from the very beginning of AWS) to use these CPU's. It still won't replace everything, but it certainly lowers their reliance on over priced, insecure, and slowly developing Intel CPU's. For AMD this endeavor by Amazon is so expensive that their requirements on production were probably numbers AMD would struggle to keep up with. Which probably played another part in Amazon going this route.