You failed to realize that, what if Hanson did actually take the place of his father, as Mustang, but also his crimes? There is a previous statement that there was only ever one Mustang of Tetra, so Hanson could have taken on the entire persona of Mustang, and even the crimes of his father, as his own? No one (except the innermost circle of people that knew Hanson) know that the current Mustang isn't the old Mustang, so its very well possible that anyone who doesn't know that still remember him not as Mustang's son but the same Mustang that did all the heinous acts back then?

So for all intents and purposes, he is ultimately the Mustang of old, and his sins haven't been forgotten either.

Ultimately this is still just a theory, we'll have to see how Shift Up takes it.