What drives a poor reputation for the Rogue class?

[LudicSavant]

The rogue can also hide in the Heavy Obscurement of the Noxious Smoke, or in the Light Obscurement of the volcanic gases with something like Skulker.

(assuming the dragon is trying to keep its distance to strafe and use its breath weapon attack, otherwise Blindsight is in play).

If it wants to strafe the party with an AoE, it doesn't need to see you in the first place.

If it actually wants to go for you in particular (despite the relatively low threat of a post-round-one Assassin), it's coming at you with 60 foot blindsight.

the assassin can Impersonate one of these people, and kick off the encounter with an Assassinate, shaving off almost 1/3 of the dragon's hit points in turn 1.

If a tier 4 single target alpha strike specialist with prep time gets Surprise against me, I'd count myself lucky if that was all that happened to me.

Also: If you want to finish that fight, you need to find a way to bring your party along for the infiltration.

Against an ancient dragon, a high level rogue could potentially steal a dragon egg and potentially lure the dragon to fight outside of its lair.

And so can other classes. An Assassin's skill checks and noncombat toolkit are not actually that hard to compete with.