Harry might not be able to touch Uriel normally, but we know now that the Eye of Balor could kill Uriel. Which means Uriel would have to defend himself or evade etc. Assuming he somehow didn't know the attack was coming in the first place. Uriel also, like any other immortal, can be killed on Halloween. So Harry's chance of killing Uriel isn't nothing with the right preparation. Choose the right ground, the right time, the right weapons etc.
I don't believe this to be correct. There is no reason to believe Uriel can be killed on Halloween. Just as Bob said that Walkers are unkillable, so is Uriel. He's not even here when he's talking to Harry. He's projecting a tiny peice of himself. Not only that but Halloween is about changing masks, which is why things like Mab can be killed. Uriel isn't a mask to be exchanged but a celestial being. Finally, the eye wouldn't even kill Mab. It would kill the mortal wearing the mask, Mab would move on to Molly which is why Mab told Harry to kill her if she died. Uriel is pure soul, there is no mortal beneath it to kill.
Not all Immortals are created equal.
WoJ:
Though for the record, the Dresden universe angels have been around since before time was a Thing. #TemporalHipsters
Jim: 1) A being like Uriel doesn’t really do battle in the sense of contested violence. He just sort of thinks about annihilating galaxies and it happens.
Perfect example of Mab's power vs Uriel... Not even in the same galaxy when it comes to power. Not even remotely close. Mab's power are global, Uriel's powers are on a universal scale.