There is no density problem at all.
Fusion is estimated to be around 10 million times more efficient as classic fossil energy.
Basically it looks like this:
Fossil x1 million ~= nuclear fission x 10 ~= nuclear fusion x100 ~= matter/antimatter annihilation
You are correct with regard to energy production. Transfer, storage and consumption are where density becomes a problem.
Would you rather live in the stoneage?
Yes, I think the late bronze age would be a very fulfilling time to be a human being. I understand and accept that this is a personal aesthetic opinion, but I find it far preferable to the miasmatic dystopia I observe around me.
I mean with fusion energy abudant we will be able to colonize space and at least have an exit strategy in case our earth is destroyed.
in case?