Garrosh was so much better of a villain then Sylvanas, for more reasons then you might think. First off let us talk motive, He was an over-eager general in wrath turned war hero, but he didn’t want the position of warchief, as he knew he was not a governor, still thrall gave it to him in the middle of a resource crisis, and the twilight hammer plotted to remove all trade between the factions.
Despite this, his villainy was very much of his own making. As he was never a governor or politician his response to any problem was warfare, and despite having some standards, it was made from just as much hatred of the alliance as necessity of the horde. He also was very racist towards trolls and the undead, viewing the former as weak cowards and the latter as unholy abominations. Garrosh’s overly agressive personality also lead to him alienating his allies.
Meanwhile Sylvanas’ motivations seem to boil down to 3 things, she hates the idea of hope, she is overly paranoid someone might overthrow her, and she is in league with death. Thats it, not nearly as human as Garrosh’s aggressiveness and prejudice, and most of it really comes out of left field.
Now for how they handle their tactics. Garrosh as a general isn’t honestly to impressive, but he is a fairly skilled manipulator by the end of the day, He manipulated Baine and Jaina to kill as many alliance generals as possible during the siege of theramore, then abused Jaina’s mental instability to make it so when he steals the divine bell, she blames the sunreavers shutting down any potential peace talks between her and the blood elves. However he was very hotheaded when coming up with strategies, such as in the twilight highlands when he got his airship shot down, and his tendency to give supply caravans the minimum defenses possible, his pride of Orcish superiority also is a major reason he was overthrown, as he managed to piss off each individual race of the horde in ways that could have easily been avoided, with the narrative acknowledging his poor impulse controll.
Sylvanas meanwhile doesn’t even really have a plan. She kills people for little to no reason in order to win a war she started for pretty poor reasoning. From killing forsaken for not immediately returning to her side (or being to slow), to ruining a hostage situation because a dying night elf said she wasn’t afraid of her, she never really manipulates people that well. You can’t just say “JUST AS PLANNED” to every setback then never reveal how it works to your advantage, that just makes you look dumb. The narrative also seems to pretend to ignore sylvanas is extremely controlled by her impulses in BfA.
Finally, their crimes, garrosh’s crimes were many, but he only hit the really big ones like genocide towards the end of his reign, even theramore i struggle to call a genocide because he knew they got notice beforehand and would evacuate the city. It’s not until seige that he crosses that line as a final “Look at how #%@$ up this guy is” after we had plenty of confirmation he was evil. He previously used evil actions that, while not as big in scope as genocide, are easier to process. Oppression, Sacrificing Allies, Aggressive Expansion, Imperialism, Not paying his workers, Assassinating political rivals and potential dissenters. Sylvanas’ evil is genocide, one very stupid assasination attempt, and brainwashing jaina’s brother. Oh and arresting Baine, but only after he committed treason. Yeah that’s the issue. while Genocide is one of the most evil things one can do it is also harder for most people grasp the severity of. A Million is a statistic after all. And the Assasination Attempt on Thralls family makes literally no sense, your sending to assasins, to kill a mans entire familly, when said man is living in a self imposed exile and has never shown disapproval of your rule, across PLANETS! Her evil never feels like it has a reason, yet are never small enough for their pettiness to work.
Oh and finally, they didn’t pretend for half an expansion Garrosh wasn’t evil after he started doing mega-evil stuff.