The Beast and Angelus were pretty dim, though! The Beast literally makes the only weapon that can kill it, and Angelus decides to use the weapon, even knowing doing such might return the sun. Not liking being told what to do is one thing; trying something that might actively make life more difficult for yourself is another.
It was such a contrast with Angelus.
In the cage he's this psychological Hannibal Lector esq villain who tricks Gunn into revealing the murder of the Professor.
Out the cage he's an idiot who literally spends his time either boasting at the bar or like you say doing stupid things. Like how did he not know what Faith was trying to do when she swung those mental chains it was obvious.