Lew Sorley correctly states that Thieu was arguably a better president in his context than LBJ was. In the latter part of the war, after Abrams was put in charge, there were many successes with the ARVN and a number of skillfull eliminations of the corrupt and incompetent leaders and elevations of the more talented and less corrupt. Other than Sorley very few have really examined this. Read "A Better War."
I've seen Sorely extensively in a video series called "The Long Way Home Project." He's very good.