Bob spent a long time swirling around Eihniu during the binding, which could arguably be Harry's largest working yet. One of Harry's power sources was the Spear of Longinus, an almost sentient holy relic. I wonder, how Bob was effected by the power of the spear? an upgrade? Or as a spirit of intellect is he immune to it's influence?
Bob once said that there were some things of a spiritual nature that he couldn't go near. He said he would be crossing lines he shouldn't or couldn't cross. It's one of the early novels. (I just remembered. Harry wanted Bob to find the Shroud of Turin.) So, I don't think the spear had any impact on Bob at all. His physical proximity to the spear did not mean he was interacting with it in any way. Bob might have learned something about Ethniu and how her power works that he didn't know before. So, it's possible that in some future novel Harry could decide to unleash Ethniu on a more dangerous enemy and Bob might provide Harry with some advice on how best to control her. I'm not predicting that will happen, but it's one way Bob being around Ethniu could be significant.
I haven't see anyone mentioning this possibiity: Harry can take Titanic bronze
It might take a Titan's willpower (or as Harry put it, denial power) for whole body armor, but if it can be broken down to smaller parts, then it could be manageable. Besides, we don't know enough about starborn.
What we do know about starborns, which isn't in great details, is that they're anomaly once every 666 years that can defy Outsiders.So yes, we literally don't know enough
No, we don't know if that's necessary for starborns to defy gods or anyone else, that's why they're anomalies