Punishing the father by killing his son is morally wrong whatever the father did but I do not think the Uriel who killed the firstborn is the same as the Uriel who walks around now just like the Odin who demanded human sacrifices is not the same one as he who talked with Harry.
They change because the stories about them change.
Nope - at least, as far as Uriel's case. By WOJ, the reason angels are not susceptible to Nemesis is that their nature is absolute. They're not subject to change such as that based on drift in belief the way pagan gods and 'worshipped' Fae (i.e. those in a position like Kringle who mortals believe in, even if not explicitly religious figures).
And I fully admit if it ever turns out that Nicodemus is doing this just to get personal power I'll admit he is E evil, but from all the hints we have so far it seems more than likely that Nicodemus has an end game goal that fights the Outsiders. Which we also use to justify all that Mab does, so again they are at worst equal.
Oh, power is definitely a means to an end for Nic as well. But the difference between him and Mab is that keeping the Outsiders Out is Mab's overall purpose. I'm confident Nic shares that as an objective, but it's not like if someone were able to use a WMD to kill everything beyond the Gates, does anyone really think he's just going to say "mission accomplished" and retire to take up gardening? He's still going to have his 'saint of hell' game plan to act out.