Its not speculation. Evidence suggests so. Unless you have counter arguments to disprove the evidences put forward, your argument is moot. Yes, Minato said that chakra or seals were required to teleport. But, how on earth does that have anything to do with teleportation radius?
are you suggesting susanoo is a thin layer and then empty? it is full of chakra which is why sasuke or madara can float inside. unless you break it or they are touching the ground, they are intangable
High concentration of chakra is used to maintain susanoo. I dont recall any part that mentions about dense chakra being present inside the susanoo. Using S/T ninjutsu, Minato basically circumnavigates the highly-concentrated chakra barrier that is susanoo.
I didn't say anything about not having to mark his target. I dont know what part you're talking about, certainly not anything I said.
Are you trying to imply that Madara or Sasuke is intangible inside the susanoo? Now that is hard to buy. Ground connection was required for Gaara because he uses sand. On the other hand, space time manipulation is still viable because Madara is not incorporeal inside the susanoo, merely inside a barrier, a physical barrier made from chakra. There's hardly any difference from susanoo and the barrier of four suns in that case except for the fact that barrier of four suns is merely a defensive one whereas susanoo can also be used for offense.