Most recent ARM PCs were explicitly low-power low-performance. That was the goal, not a description of the architecture. The mobile part pretty much confirms that.
The ARM chips that Amazon is putting in the servers is nothing like what you'll find in a consumer arm laptop.
Surely these are in development, but based on the ARM experience, it'll be at least 5 years from availability of reasonable parts to any decent volume.
Depending what what performance level you're looking at, they're a very large fraction of the server cost. Get a dual or quad socket board and buy the higher end CPUs and you might be looking at well over half the cost.
Its possible to shift this argument different ways depending on the part of the market your looking at.
Intel stumbled in fabrication and complicated architecture is having a bit of a growing pain. The CPU market doesn't make revenue like it used it – very few desktop users feel the need to upgrade every two years and for many applications pretty much any CPU is fast enough. Growth in the cloud market could be good, but any thing that threatens their market share of the cloud is threat to Intel.
The only ARM based PCs I've ever seen are the Raspberry Pi and other products intended to compete with the Pi, and one of the core features of these PCs is being a complete computer for under $100. Keeping the price low was always the top priority, not performance.
https://www.scylladb.com/2019/12/05/is-arm-ready-for-server-...
Maybe it’s a latency vs throughput thing?
As far as I know, ARM is great at balancing latency and power consumption, but behind x64 in throughput. [citation needed]
https://www.scylladb.com/2019/12/05/is-arm-ready-for-server-...
Every ARM based PC I've seen has been disappointingly slow, which I dont really understand because phones usually are amazingly quick.
DEC Alpha, Sun Sparc, MIPS, PowerPC couldn't keep up with Intel in the recent past either.
Intel CPUs aren't cheap, but they're a fraction of the cost of a server.
All adds up to interesting innovation but not necessarily the future.