the laptop always does this; it's not something where it magically (and mysteriously) gets slower as it ages. it's also obvious when this is happening, even if not directly indicated: the fan will be cranking and the laptop will be really hot to the touch.
and, there's also somehow more of a feeling that a phone is a controlled system that will "just work," whereas computers/laptops are always screwing up in one way or another...
In some ways that does happen. As computers get more lint in them that often start heading thermal barrier’s and automatically throttling themselves without telling the user.
As for whether the fan makes it obvious I guess that depends on how loud the fan is. Or this could happen to a desktop that you just have placed out of the way enough that you can’t hear it well.
I'm not sure what you mean by this, but you can run software that will give you these details and much, much more about the state of the CPU.
https://randomascii.wordpress.com/2013/08/06/defective-heat-...
If you have a laptop then I have bad news; your CPU throttles itself. Especially if you play games.
It gets too hot and slows itself down to prevent damage. There’s not even a direct way to detect this. Which I do admit is annoying.
Apple deserves this PR egg on their face. But they aren’t doing anything super wrong. Additional battery life info will go a long ways towards doing things right.