> We don't need nuclear, because we have other options for firm low-carbon energy (geothermal) and energy storage of surplus and super-cheap intermittent renewables (lithium ion, flow batteries, hydrogen, methane, compressed air, liquid air...).
Nuclear power is a zero emissions source of power. Alternative renewables (e.g. wind, solar) require fossil fuels to power the electrical grid when they are not able to generate power. The sources you mention are also substantial less effective from an energy density perspective. The amount of energy they output, relative to the energy input to construct them and the amount of land they consume, is orders of magnitude less than that produced by nuclear.
Storing energy is incredibly expensive. If we were to use lithium ion batteries to store electricity, it would cost trillions of dollars to produce and maintain the batteries. This does not include the immense environmental damage that would occur as a consequence of this policy (land usage, mining, waste products, etc.)
> If nuclear could compete on cost, we should go for it, but it can't without a major tech breakthrough
Nuclear energy is more cost effective than alternatives. The main issue is that antinuclear activists, funded by the fossil fuel industry, have lobbied to make it cost prohibitive to build nuclear power plants by way of onerous regulation and prolonged legal battles. Countries that have reduced their reliance on nuclear power, for example France, have seen their electricity prices and carbon emissions rise as a consequence. We also know that nuclear power plants can operate for longer than previously believed — at least 80 years, as opposed to the 40 years that was previously assumed. This understanding further drives down the cost of electricity derived from nuclear energy, as it reduces the need to construct new facilities.
> For example, we will definitely need to start producing hydrogen
Why? Producing hydrogen is inefficient and unnecessary if you have a consistent source of energy, which nuclear provides.
> As it is, it's a dinosaur from the past, a legacy of a time before we had better tech.
Nuclear energy is safe, causing fewer deaths and adverse health impacts than alternative sources of energy. It is cleaner, cheaper, and more reliable than alternatives while also being far more environmentally friendly. If it is a dinosaur, then so are the transistors that make up computer processors, which are roughly as old and somehow are still the subject of cutting edge research.