You are right but I feel you're missing a crucial point. You can't ignore all the work that went into the creation and expansion of Skyrim. The work was meant to make the game "yours": you're the master of your destiny. That's why I say it's hardcore.
Let's take another poplular rpg game: Witcher 3. It's way easier to take a game like Witcher 3, put in 100 hours then put it away forever. Not because the game is not on par with Skyrim: it is as deeply created and relies on lore presented on previous games, just like Skyrim.
But it is not as hardcore: you play a determined role, you're not creating the character and the storyline, like in Skyrim. Once you have lead Geralt to his victory, the incentive to replay are very low. I'm hardcore and I sure didn't play again when I defeated that guy:
The game was awesome and memorable but I uninstalled it after. You can do that with Skyrim too. But you're purposely avoiding a lot of things. Skyrim is a role-play game: the goal is to create your own custom character, role-play the build and choose your missions depending on the build. I gave multiple examples of that but this one is easy to get: You can play 100 hours as a Kahjiit merchant who rarely enters town, builds a house in the wild and travels around Skyrim to buy and sell contraband Mood Sugar.
Then, you can start a new character. Let's play an Imperial legionary this time! Son of a Solitude military officer, he rarely goes wandering in the wild like the Kaahjit: he's a city guy. He will want to become thane of each hold, buy a house in every town and make his father proud. He's gonna enter the civil war questline (the Kaahjit never touched it) and follow it to the end. He will then decide if he goes the "Dragonborn" way or if he just goes for glory.
The 100 hours you play with the Imperial will be totally different. If you were to always create characters to complete the main quest with fetch quests around, there would not be incentives to replay the game. But that's not what Skyrim is about, at all. In Skyrim, you can play 100 hours without even touching the main quest. I don't think you can do that on Witcher 3: you have to follow the story line to make the game progress.
Everything is possible in Skyrim, you're the sole master of your destiny. That's not the case with Witcher 3: it's a game with a determined goal. Once reached, the replay factor is very low.