Use One Big Server (2022)

This isn't even the end game for "one big server". AMD will give the most bang per rack, but there are other factors.

An IBM z17 is effectively one big server too, but provides levels of reliability that are simply not available in most IT environments. It won't outperform the AMD rack, but it will definitely keep up for most practical workloads.

If you sit down and really think honestly about the cost of engineering your systems to an equivalent level of reliability, you may find the cost of the IBM stack to be competitive in a surprising number of cases.

no. In the short time I work at a z/OS-shop, they had to IPL twice. And the IPL takes ages...

Now, if you can live with the weird environment and your people know how to programm what is essentially a distributed system described in terms noone else uses: I guess it's still ok, given the competition is all executing IBMs playbook too.