I think in a way it's good that we didn't do that in the sixties. Nuclear reactors are a lot more advanced and safer these days. Probably never too late to get onto it.
The problem space we're in now is multi-dimensional. Purely on economic and rational engineering grounds you are right. Bring politics to the table and no, there is no clear time now or in the future where it will "work" to propose nuclear for powergen, where if we had installed the worse, 2/3 gen stuff in the 60s we'd be arguing about replacement, but with a good investment in nuclear physics engineering, and baseload supply demands which had displaced brown coal already.
The cost of PV and Wind (with Storage included) is already vastly lower than any commercially available Nuclear Power design.
They're also a whole lot easier to deploy and maintain, don't come with all the risks involved in current Nuclear Power designs.
There is no future path where even SMR can arrive at price point and power rating to replace the overbuild of wind and solar with storage, which provides the same energy reliability. Overbuild sounds negative but it's not: you need more than nameplate power and more units widely dispersed to avoid outages from local weather. With that comes more for storage, more for H2 conversion, desalination, other uses.
Basically, we should be further along our de-carbonisation. It's all about the past.