Shar is one of the most evil gods in the D&D pantheon. Way worse than even Lolth.
Setting aside the rest of what you say (some of which has merit, especially the last line), this is absolutely not true. Shar and Lolth are both evil deities; Shar is a Neutral Evil greater deity (the goddess of darkness) while Lolth is a Chaotic Evil lesser deity (the Queen of Spiders and goddess of the Drow, and once the elven goddess of destiny). You cannot directly compare how evil they are; but Lolth has certainly perpetrated much more evil as the tyrannical ruler of the Underdark.
Seems like you don't know FR lore that well. My comment has nothing to do with NE v. CE. Those definitions matter only in the cases of players playing the PnP game. In FR lore, the authors of that lore don't really care about "NE v. CE." Lolth has done a lot of really nasty things, but the impact of what she does is actually very limited, generally limited to only the Underdark of the Realms and not even to the Realms overall. By contrast, Shar's singular goal is to destroy the entire multiverse, to end ALL life in the multiverse. There is just no comparison. Shar is the greatest evil in the D&D pantheon. Heck even Bane, who is LE, has a much greater impact with his evil ways than Lolth. So whether they're chaotic, neutral, or lawful does not matter that much. From an FR lore standpoint, what matters is the extent to which each individual god's evil ways impact the setting. And there, Shar is the worst hands-down.
I think you're the one who is in the dark about FR lore. Your argument is incorrect on two fronts.
1. Saying that Lolth is less evil because the consequences of her actions affect fewer people is like saying that a serial killer is less evil than an embezzler. It's not a valid comparison, simply because Shar is far more powerful than Lolth, and plays on a very different stage.
2. Shar's goal is NOT to destroy the multiverse, and she is definitely not the most evil god in the multiverse. To begin with, she is a conqueror, not a destroyer. Her primary goals are to let darkness overtake light (i.e. defeat Selune and take over her followers) and the related goal of gaining control of all magic (to which end she built the Shadow Weave and attempts to corrupt the Weave). Her carelessness in how she went about this has led to drastic consequences such as the Spellplague, which is a big part of why she is reviled. But she does not actively seek to destroy the world; rather, she was one of its creators and even helped save it by aligning with Selune and the other gods during the Dawn War. Even her war with Selune stems from Selune's creation of the Sun, which led to theor original conflict, which in turn ended with the creation of many of the other gods and the banishment of Shar.
Not saying I agree with her actions, but she is far from the most evil god in the pantheon, although she is probably the most powerful of all the evil gods.
