re: If Luke has these great Jedi powers, then why is he dragging his near dead dad?

The Emperor was deliberately creating a moral choice for both Luke and Vader. A Xanatos Gambit if you will. Luke defeats Vader, he gains the stronger Skywalker as his new apprentice. Vader kills Luke, then Luke wasn't strong enough anyway and there is nothing to redeem him (neither the Emperor nor Vader knew about Leia until the "Your thoughts betray you" line)

Remember Vader was weakened anyway (The volcano had dampened his force potential from Chosen One down to just above average Force user).

Palpatine also thought that by killing Luke in front of Vader, it would extinguish any thoughts of redemption through his son that Vader might have been entertaining.

Remember Sith constantly violate the rule of Two in order to betray each other. See Galen Marek and the Emperor's hands.

And Luke had trained a few days with Ben, a couple weeks with Yoda. He was still basically a 20 yr old Youngling in Jedi. That was why his Jedi Order was so different. He established it based on the limited Holocrons and journals he could find. Plus visiting other Force sensitives like the Night sisters.

It has never been directly established but the way Luke's New Jedi Order was established it seemed that not only Obi Wan but Yoda learned from Qui Gon's force ghost. Luke likely as well, because the NJO certainly resembles Qui Gon's Living Force Philosophy in their theology.