I'm not sure what benefit density provides, especially since people obsessed with density seem to only focus on the reaction chamber, which is the smallest part of the massive building and heat rejection apparatus that will be needed.

Rejecting waste heat is a real difficulty, and part of the reason that's France's fission fleet is at less than 50% capacity right now.

Thermal electricity production has a chance of becoming obsolete compared to direct conversion of photons into electricity. When solar plus storage costs less than steam turbines plus heat rejection, then it doesn't matter how cheap or dense the fusion part is in terms of economics.