The issue is that utilities spend more than 50% of their incremental operating expense getting that electron to you, not making/buying it in the first place. With that kind of cost-stacking, nuclear has little hope of competing with solar.
The "solar makes nuclear useless" line seems wrong. There are situations where solar isn't feasible (like in a spaceship or on a boat or submarine). There also may be space, reliability, and weather limitations that make solar less attractive. Finally, we're making solar panels very fast, but if we really go all-in, it will take a long time to build as many as we need. It's probably better to hedge our bets and build nuclear now.
Re: Helion, I'm skeptical that their fusion reactor will ever be commercially viable but am not an expert and would love to be wrong. There's tons of Helion skepticism on the internet you can find if you look around.
Yes, we have some parts of country with small population density, but their share of energy consumption is also small, so they are not affect whole balance much.
I must admit, things are constantly change last months, so future could be very different. But just now, nuclear are cheapest in Ukrainian energy balance.