Fusion will have absolutely no part to play in decarbonisation because fusion is not going to be ready at scale in time, ie the next three through thirty years. Best guess is a first industrial plant selling power to the grid is going to be 2050 or so. We can’t wait till then.
Maybe at some point after that, fusion can take over from solar and wind, but fusion has major disadvantages that you’re skipping over: it’s centralised with all the political, regulatory, financing and single-point-of-failure risks that brings; and above all fusion WACC is going to be massively higher than renewables + storage + distribution. Especially when you consider how build costs for renewables and storage are going to continue to fall in the years up to 2050.
And you’re being altogether far too blithe on opex for fusion. 14MeV neutron fluxes are quite challenging, what with the embrittlement, swelling, activation, first wall replacements, superconducting magnets, tritium handling systems, cryogenics, robot replacement systems, etc.