Chemically, Sodium and Lithium are very similar, so any improvement that applies to one should be pretty applicable to the other. That’s actually one of the main strengths of Sodium batteries - most of the research that’s already gone into making Lithium batteries can be reapplied with minor tweaks. However, Sodium is inherently larger and heavier than Lithium, with fewer atoms fitting into the same space and those atoms weighing more. If research for Sodium batteries catches up with Lithium ones, they’ll still be worse just because of that, and at that point, research would get easier gains from improving Lithium batteries than Sodium ones.