My PC has been on 24/7 since I got it, which was about 4.5 years ago. The only thing to fail was the Corsair H100i but that is common, from research. (and they do have 5 year warranty)
I stream Plex and run World Community Grid 24/7.
Also just so you know, electronics don't run out while being "on" they run out as you said, by being turned on and off.
Like a lightbulb, if it is always on, it won't blow, if it is turned on and off, it will blow. This is very common amongst switch mode power supplies, especially in electronics like cable tv boxes, tv's etc.
I have many years of replacing these components. People always used to say, it was working fine, then they turned it off at the wall and it never came back on.