Can someone kindly explain to me what's the problem with Cassiopeia?

I went against some and they are EXTREMELY deadly, which was so cool! The damage and pressure they give was beyond frightful and that's what I like about it cuz it brings out a snake vibe >:)

So I asked the enemy what was the deal with cass and people were saying she has no mobility or "escape" and that her kit is silly because all you're doing is Q E E E E Q EEEEEEEEEEQ EEEEEEEEEEEEEEEEEEE QQQ!!!!!!WW!!EEEEEEEE!E!!!!~!!!DEISfh'udxcbgfhjdxcbgjhsfdg

:l