I think people need to let go what happened many decades ago, whether Thor was bulletproof or not, doesn't really matter, he is now. Hell i remember Hulk had literally no healing factor back in those times but nowadays he has one of the most broken healing factors in Marvel, things change and evolve.
Even though Stan himself wrote the instance above where Thor cant be hurt even by atomic blast, he also wrote this
and this
So not even back then were comics that consistent nor did writers care that much about power levels as we'd like to think, so just leave it at that and move on, you can't change the past.