Anakin Starkiller said:
I personally can’t stand the idea of Rogue One being Episode III.
The characters just don’t match up. Anakin has what is effectively a glorified cameo, Padme is dead, and Obi-Wan is entirely absent. It’d be the equivalent for ROTJ getting rid of Han, restricting Luke to a cameo, and having Leia be on the other side of the galaxy absent.
However, RO could work as a trilogy of anthologies leading up to A New Hope. The first would be a three in one PT which explains Anakin’s backstory. The second would be Solo, explaining Han’s backstory. And the last would explain the plot of Episode IV. In that sense it could work- but not as a proper episode to the Skywalker Saga.