> A 3 year depreciation cycle may be reasonable for some spaces but not others.
Exactly.
I am running a server at Hetzner which has a CPU that was discontinued about 7 years ago. I don't know the exact age of the machine because it was already used when I got it 4 years ago, but based on the CPU availability it's at least 7 or 8 years old, potentially even older.
Nothing on that machine has failed in the last 4 years except for HDDs (the spinning platter type), which are immediately swapped when broken, RAID rebuilds, everything's fine.
3 years is no time for hardware nowadays. It can live much longer, especially if storage is solid-state. And the performance improvements often aren't substantial enough to warrant a swap within anything shorter than 5 or 6 years.