See fusion this way: it's like a coal power plant with infinite free coal (because the rest of it is the same - turbines, water treatment, condensers, generators, power transformation and transmission - and thermonuclear reactor will for sure never be cheaper than a coal-fired steam boiler). Which means, electricity cost will be same as of a coal plant minus the price of coal. Which will already be above cost of most renewable sources and, once electrolyzers for green hydrogen will start coming online, remembering that barely 15% of renewable electricity will need to be passed through them (rest can simply be balanced by different renewables), will still be sort of competitive.
And we don't have fusion yet, while renewables will keep getting cheaper.