PV capacity factor is typically 16%-28% [1], which adjusting the W/kg, gives us:
Solar PV: 0.8W/kg - 2.8W/kg, capacity factor adjusted (with supporting infrastructure weighing 2x the panels, a total spitball)
Nuclear: 0.8W/kg - 4.5W/kg, capacity factor adjusted, two different modern reactor designs, concrete only.
With this ratio, higher numbers mean better power densities, and the ranges completely overlap between nuclear and solar PV. Nuclear isn't achieving orders of magnitude better power density over solar.
No one claimed an order of magnitude better. Nuclear looks somewhat more sustainable than renewable, and it can do some things renewables can't.
We should be doing both.
How can one even imagine a space-faring civilization powered by wind mills?
Which puts solar and nuclear on completely the same scale...
If you don't think mass is a good way to compare, and you're concerned about resources, please suggest the metric that will somehow make nuclear look good. Because that concrete is not very recyclable. So the 95% recyclability of solar panels is making them look a looooot better than nuclear once we move beyond mass to something more nuanced.