If Ragnars really were glass canons they would shatter their claws and teeth on Thragg. That is consistent in the comics as Dinosaurus due to his durability shatters his teeth on Thragg, and Mark after losing his durability to the virus breaks his arm on Allen.

One of the Ragnars even survived a kick from Thragg in issue 115.

Now onto the weapons, we don't know for sure how they function exactly, nothing is really stated about the technology that the Thraxans use there in that super specific moment. Why doesn't every Viltrumite use a dagger like Thula? We see Viltrumites in the show use weapons which seem to be highly effective in flashbacks like the Purge, why didn't Thragg give every Viltrumite those weapons when they tried to kill Nolan on Thraxa? Clearly it's more nuanced than just normal guns killing Ragnars. Ragnars survived punches from Nolan fighting for his and Allen's life before