Surprisingly power is a huge factor. Spinning up 48/96 drives on boot can surge beyond what power supplies could handle, so things supported staggered spin ups. This allowed huge banks of drives to start without blowing a power supply, but you don’t know how many drives or if staggered spin up is enabled until it times out. This was a huge boot delay for servers.

That's interesting to note, but I'm just talking about computers with 1 drive connected to them. Both for the servers and the laptops. In fact the older (faster) laptop had both a DVD and an HDD, whereas the newer one just has an SSD...

Probably because no one turns anything off anymore so the selection pressure is gone.

So I'm not so sure about that. When I complained recently about sleep issues on my windows 10 desktop I was met with an overwhelming "but....why are you sleeping your desktop? Just switch it off like a normal person?".

Indeed. I've no idea if sleep works on my desktop. I've never tried.

Today we have to make things hack proof, noob proof and lots of proofing adds more complexity, cost and lowers speed.

I don't think this is it. I haven't tried with many machines but I don't think current machines are all generally slow with firmware, just some of them. The part that baffles me is that the slowness is on the faster ones.