The biggest problem with fusion utility-scale power is that it doesn’t exist. It may not ever be feasible. Or we might figure out how to make fusion power at scale, but not cost-effectively. It’s all unknowns at this point, and it’s been that way for 50 years. Progress is being made, but we don’t know yet how to get to the endpoint of utility scale fusion power.
Therefore, the responsible thing to do right now is to ignore it for the purposes of planning out a near or medium future energy grid. If fusion power were to achieve net breakeven tomorrow (it’s not close), it’d still take decades to develop and prove out large power plants based on it.