No, you're probably mixing two situations and coming to the wrong conclusion. Chances are good that when you did your Windows 8.1 to 10 upgrade, it was with an earlier version of Windows 10. And that version of Windows 10 ran the SP2 hard (seen as hot, constant fan usage and heavy battery drain). The ISO/USB that's available now is the 1511 version which runs better. In fact, each update of Windows 10 is running better and better.
I did a 8.1 to 10 upgrade on my SP2 at the very beginning to register my SP2 so I wouldn't need a product key anymore. Than I clean wiped the machine to 10 (the first version of 10). All the problems that people complained about even after the clean installation. But now with the newer updates of Windows, Windows 10 is starting to perform well on the SP2.