The problem with Diem is IIRC that:
1) His blatant Catholic favoritism, though popular in the West, is deeply controversial to say the least in a country that is 90% Buddhist, which means his natural constituency in 1963 is minimal
2) He's one of the few major contemporary RVN leaders who does have genuine nationalist credentials (being exiled or harrassed by the French for refusing to play along) and who isn't a Communist.
A surviving Diem is probably something like pre-2011 Bashar Assad - willing to tolerate corruption from his family and friends, autocratic, a sonofabitch, but in power because the alternatives are not palatable either.
So I'll go with "slightly better" but that's a pretty damn low barrier there.