Sonically they could be the same. Although most times they are not.
I see the selling point of a pre/power amp is versatility. You buy the switching and controls you need and select the power you need. With an integrated you have to buy what is packaged together.
At least that is the way I sold them in the 60s and 70s.
I like the idea of having separate components for everything... but I find it makes upgrade-itis worse because now there are more mix-and-match possibilities