(1) Knocking Luke out without combating him doesn't demonstrate a superior spiritual power, it only demonstrates superior tactical judgment. ESB Luke certainly is at the point of concentration -- he's out there lifting stones and droids while upside-down, no less, and he's already focused enough to concentrate for telepathy even in a life or death situation. The whole point of Vader trying to get Luke in a carbon freeze was to take him unharmed and also avoid him doing anything tricky like using Force powers on Vader's mooks. Vader torturing Luke's friends in front of him doesn't demonstrate the power of the Dark Side, it just demonstrates that Vader is a jerk and even less to be trusted or allied with. The Dark Side, per Yoda, is "quick to join in a fight." That's what Vader is counting on, that Luke will reach out for the Dark Side in battle against him. (2) Like I said, in ROTS, for one moment, during the Warner Brothers cartoon duel between Luke, Dooku, and Anakin, Dooku uses Force choke on Obi-Wan before flinging him aside. It's set up and implied as a sort of sucker punch, that Obi-Wan wasn't ready for it, which in turn implies that a prepared Force user can counter it. Either way, Vader didn't invent it. But I'm setting aside ROTS because I'd rather try and figure out Vader's motives from within ESB or the CT as a whole than bring the PT into it. (3) Where does it say in the film that becoming a cyborg diminishes a Force user's power? That's nowhere on screen. And IIRC even the EU says that chopping off or immolating limbs doesn't really hurt your Force potential because it's the midichlorian concentration in the blood that matters, not whether you lose 10% of your cells due to some dude with a lightsaber doing a Black Knight from Monty Python.