I am biased against Muster, as I can not stand the guy, so I am best to limit my comments on him. I do think he is overrated by a lot of people though, his weakness on non clay surfaces, often make people overrate the level of clay courter he was.Muster is ridiculously overrated. Thiem basically only has to win one FO to overtake him. And I don’t like Thiem at all. Whether he can win this FO Titel is yet to see but given the clay field I wouldn’t rule it out once Nadal and Djokovic are out of the picture.
I will say his dominance level of 95-96 was scary and super impressive, despite the blunder at RG 96. Although he may have also benefitted by not having any of Courier, Bruguera, Kuerten, being at their best those days years, and while the clay field was adequate, it may not have been as strong as most other years of that decade. I also strongly believe he was using excess PEDs for a couple years around that period, which would explain his almost superhuman temporary rise in fitness and endurance, but that is another topic, and I know some other that for Nadal, Djokovic 2011, and some others, so probably best to not delve too deeply into that.
His record against Bruguera is impressive, but record against Courier (sans 97 when Courier was a shadow of himself) pretty awful including on clay, and record against attacking players who arent even good on clay definitely a big negative.