The massive expense is, in the scheme of things, actually quite small. But there's no "there" there with fusion energy: the lower bound on its cost is the cost of fission energy.
Yes, in theory, if you could convince the world to accept thousands of new fission plants, you could probably get the cost pretty low, and that low cost would be pretty close to the same outcome for fission. But, good luck with that! Fusion has a much better chance of actually achieving the theoretical long-term economics of fission.
The list goes on. The more you look, the worse it gets.