There's still people out there treating *Game of Thrones* as their main historical reference. There's more people out there relying on ChatGPT. Under the circumstances, getting your history from Gore Vidal ain't too bad.
It is a pretty good one. Otherwise, see @metalclassicist.bsky.social , Shaun Tougher or Robert Browning (Glaswegian Ancient Historian, not 19C poet), for readable works on him. There's also the 3 vol Lœb edition of his works.