Important doesn't mean "smart." I would actually argue Wittgenstein wasn't very smart (and in my opinion, often wrong). There were just the right enough people around him that thought he was a gifted student (though he didn't always excel academically, weirdly enough). At what, that is a mystery and is contentious. During his early years when people thought that, he was already harassing and beating children (he published Tractatus in his early 30s).

1. He rejected infinite mathematical extensions, unbounded quantification, misunderstood Godel’s incompleteness theorem and quite a bit more that the math community dismissed. So he wasn't a math genius (he originally studied engineering and became interested in math through that)

2. Most people were skeptical of his picture theory, and rightfully so. It grew out of the same environment that gave rise to, at that time and in their initial form, logical positivism, empiricism, and at its most horrific, behaviourism, which led to infant pain denial. Picture theory explains something surface-level, which in itself people understood was just incomplete, and I'm sure you know, even Wittgenstein rejected his theory later

3. But the problem with his last work, Investigations, was that it was again surface-level musings, and written in a weird cryptic way sprinkled with made up words. His language-games, to me, sounds like what teens nowadays would talk about in high school with less fancy language. And it describes, to me, this kind of juvenile high school behaviour. Which, fair enough, I'm sure rings true to some people. But his philosophy is general enough to not really contribute much as a whole. It just hides behind this high-brow language. Yet he was very adamant and defensive about it

Wittgenstein had severe anger issues that people recognized but hardly anyone wanted to do much about. He had a superiority complex (lots of childhood stuff in his life probably) and he just didn't like a lot of people and thought very little of them

I guess the one good thing about him I can say is when he wanted to accomplish something he really set his mind to it. If only that same fervour was used to be not just a better person but to work well with others, he might've contributed something most experts would still rely on and be influenced by