yeah, don carlo was a clear thinker that's why he survived so long. but, bringing in the westies, castellano never had the brains Gambino had.
I don't think it was all that bad thinking.
Yes, the Westies were a bunch of (relatively) small-time junkies and drunks, but it was clear that they were crazy enough to take on the gambinos. Why risk a street war with a bunch of unpredicable crazies and would bring a lot of heat from cops when they can be
your crazies and people will be afraid that you could unleash the Westies on them.
Why do you think he kept DeMeo around for so long? He made money and everyone (even Costellano) was afraid of him. Costellano wasn't the best boss ever and he certainly was no Don Carlo, but he wasn't a dummy.