the US did not know how many people were in the house or what they were armed with, so the US brought enough fire power to handle anything.
if the US had used less firepower and americans were killed and wounded, you would say,"stupid americans , why didn't they bring more", well they did bring more and now you say "why did the americans need so much firepower", it must be easy to second guess when you don't have to make the decisions.
as a former marine , there is no such thing as "too much firepower"