That's plausible.
There's at least a third unique one, the Cheydinhall one, you never in my experience see that one again.There are two unique Oblivion maps, the first one, and the big Bruma gate with the city destroyer.
The temptation is to save before taking it, and keep retaking it until you get the feather sigil stone. Which does somewhat break the game, but it's definitely a temptation.Not that I minded that much, personally, I suppose that as long as you don't farm them over and over, they don't get old that fast. Plus I liked seeing what enchantment the sigil at the end would have.
There were some quests in Oblivion (Daedric quests in particular?) that were gated by rank.Or even the Morrowind road, you need a certain rank to unlock quests, and you need proper skills to rise in rank.