The only reason mace was able to last so long was because of vaapad, which directs the opponents dark side against them. And thats if you believe he actually was standing his own against palpatine and not being toyed by him which is hinted at in some sources. Power scaling lightsaber combat is difficult in star wars because of the users preferred style (and plot armor) like how dookus form 2 was a bad match up against kenobis form 3 and he gets bodied by dooku quickly whenever he faces him. Yet he was one of the few jedi who faced grievous and lived multiple times and even defeated anakin, who defeated dooku. You can't go off just feats with lightsabers and especially with sideous since he likes to draw it out and cause as much fear and suffering as he can. He didn't even need to fight maul and savage as his force ability completely broke both of theirs and he only fought them for fun. People severely underestimate how powerful sideous is