That's certainly been the normal historical viewpoint. I question its effectiveness. But that doesn't stop it from being the dominant concept.
Still, given how sharply Irose's home-brew warships already outclass their Star League counterparts, I think it's not something the TCN needs to be doing. It looks a lot worse for the SLN & AFFS to be beat on their own terms than to be beat with copious use of nukes, even against military targets (I didn't see any indication of the SLN using nukes against Taurian naval ships in H:RW). Using nukes lets the SLN blame Taurian atrocities for their failures, even though the Concordat didn't sign Ares. If the Taurians don't use nukes against ships, I think it'll cause people back home to say "How incompetent are you, SLDF/AFFS, that you're getting curb-stomped by a Periphery nation that despite not signing Ares isn't even using nukes on your ships." That meme would play well in the civil sector of the FedSuns and Hegemony, and probably do a lot more to undermine the willingness of those populations to support the war than attacking the civil supply-ship fleet.
On the other hand...it's always a bad idea to limit the force options of your military commanders. And, hell, the Concordat didn't sign Ares.
As for the per-capita income thing...look up modern lists of nations ranked by per-capita income, both normalized and purchasing power parity. High per-capita income has no real correlation with military power. Unless France is secretly quaking it its boots about being invaded by Luxemburg, or Iran is terrified of upsetting Qatar. Sure, nations with high per-capita incomes are more likely to have a high-tech military, but given the situation the Taurians are in, larger numbers of slightly-less-advanced equipment is probably what they need. Of course, since every significant piece of warship technology was invented more than a hundred years before the Reunification War, there really isn't a tech-curve in WarShips. Just a lot of bad designs.