I'm confused as to where the MC's mind even came from. It clearly isn't the origanal emperor, his personality and values are too different, and he considers the world where Resistance Noah is a game to be a dream. To make it worse, he's been shown to have some of the original Menas's memories, with it being a coin flip whether he identifies the original to be him or not. Just read Chapter 1.2 (pages 3-8) and 2.1 (page 4) to see what I'm talking about. Also, he's lost common knowledge such as how much currency is worth, and I think someone managing an empire needs to know at least that much.
As far as I'm concerned, he never was the 'Last Boss'. I can't get invested (or even care) at all with an MC like this.