"The Archdruid is not an archdruid but a regent" is the only one with some actual merit.
The actual archdruid is not tagged as weakened or debuffed, but as a LEVEL 5, period. Even later when at peak form. Which, aside for the horrendous idea of scaling any NPC or monster to the player's level range, leads to the secondary problem that levels shouldn't be openly displayed to begin with.
The fact that you can kill a dying mindflayer with a single HP remaining is not an issue compared to the fact that he's explicitly labeled as a low level enemy.
Having the occasional "goblin champion" wouldn't even be an issue, if not for the fact that by this game's standards that category summarizes half of the goblins thrown at you.
The red dragon shouldn't even be an actual fight (it's there just to look intimidating in a cutscene), but it doesn't change the fact that you can target it and it's labeled as level 4. The similar Red Dragon in the prologue can be targeted and it's labeled as a level 1 creature... Are you seeing a pattern here, Veronica?
Your example about the "seeing a black person for the first time" is completely misplaced, anyway, since D&D has already in place the rules for having humanoid sentient races scale across the entire range of the power levels, while monsters aren't supposed to be leveled at all (they have a challenge rating, instead).
The monsters effectively have levels, but it would indeed be better to offer a CR - but that doesn't mean that you cannot have powerful creatures around you. In fact, there should be more though most should not be made easier just because your character can come across them at earlier levels. Rather, you should be coming back to fight them at later levels or they should be handled by other higher level adventurers that coexist with your group - to create a more fully fleshed out world. Hell, what I threw at my level 3 characters in my most recent DM session was a wizard's keep along their path to fight bandits - it was above their CR and that was made apparent with the first enemy they came across outside the keep. They learned the lesson without dying and stuck to what they want - but this existed and they could opt to come back to it later.
