tr:dr; he says "x86 took over the server market" because it was the same architecture developers in companies had on their machines thus it made it very easy to develop applications on their machines to then ship to the servers.
Now this, among others he made, are very good points on how and why it is hard for ARM to get mainstream on the datacenter, however I also feel like he kind lost touch with reality on this one…
He's comparing two very different situations, more specifically eras. Developers aren't so tied anymore like they used to be to the underlaying hardware. The software development market evolved from C to very high language languages such as Javascript/Typescript and the majority of stuff developed is done or will be done in those languages thus the CPU architecture becomes irrelevant.
Obviously very big companies such as Google, Microsoft and Amazon are more than happy to pay the little "tax" to ensure Javascript runs fine on ARM than to pay the big bucks they pay for x86…
What are your thoughts?
It's odd that you're saying you shouldn't consider the specific cases where C excels and then narrowing down things to the Web, where languages like php excel. So now you probably have some idea why your experience is so narrow. There's a lot more to programming than the Web, and there's always going to be.