My guess is
Do you think me of little worth,
Hollow can be a synonym for worthless as in "hollow victory"
do I live in a tree,
A tree hollow is a cavity in a tree which may provide a habitat for animals.
I have a theory on the earth, are you on something me,
Hollow Earth Theory. Are you on something hollow?
Not the nicest thing to speak when you describe a friend,
Hollow can mean insincere as in a "hollow compliment".
Could I make a lighter load
To hollow out is to make a hole in something which would make a lighter load.
or might that break or bend,
Having a hole in something might break it. Also a hollow can refer to a concavity or depression which would appear as a bend.
And without me, a victory is said to be much sweeter,
A hollow victory is a victory that inflicts such a heavy toll on the victor as to not be sweet at all.
But with a point I'm deadlier, and maybe even neater.
Hollow-point bullets are designed to increase in diameter once within a target making them extremely deadly but also superficially neat.