If you want baseload power, you can choose between coal, nuclear and natural gas. Natural gas has estimates that range between 72 and 113, so depending on which you choose it might well be cheaper or more expensive than nuclear power. Natural gas has a number of advantages over coal, but unfortunately it is now thought to be almost as bad as coal in terms of effects on climate change - this is a very bad negative externality that isn't priced into the cost. Your original point was that "Nuclear costs are notoriously high" - instead they are projected to be roughly comparable to other forms of baseload power.

>..."not typically included in levelised cost of electricity assessments is the cost of decommissioning a reactor and disposing nuclear waste

Maybe in other countries, but not the US. Every nuclear power plant in the United States is required, by the Nuclear Regulatory Commission as part of its licensing to set aside sufficient funds to decommission the plant when it reaches the end of its useful life.

>...(The USA is an exception, because the cost of decommissioning is included in the price of electricity, per the Nuclear Waste Policy Act),

Also there is a tax on electricity produced by nuclear power in the US to cover eventual long term waste disposal so it is priced into the cost - though ideally this high level waste will eventually be burned in a 4th gen reactor so the volume of waste will be a small fraction of what it would otherwise be.