What was Ben's and Yoda's plan?
I think with the Prequels the actions of Ben and Yoda become very questionable.
The facts:
First, because of Rots they know how extremely powerful the Emperor is. He was around equal to Yoda in Rots and presumably since then up to Rotj he should be must more powerful.
Ben from his fight with Vader should have some idea of how powerful Vader is.
Ben and Yoda wait 20 years to train Luke and expect him in Rotj to take on and defeat Vader.
Why it doesn't make sense.
Ben and Yoda wait too long to train Luke.
According to how powerful the Emperor was, if Luke was every going to have a chance against him he needed to be trained from early childhood based on the power progression shown in the prequels with Anakin. Anakin started his training at age 9 and 10 years later in AOTC of formal Jedi training he wasn't anywhere near the power of the Emperor in Rotj. In fact, he was (if we can believe Anakin in Rots) half as powerful as himself in Rots. Anakin in Rots was weaker than Darth Vader at the time of the OT. Darth Vader in turn was only 80 percent as powerful as the Emperor in Rotj. Therefore, we have from the PT Anakin no where near the powerful to defeat Vader or the Emperor after 10 solid years of training, heck even after 3 more years of War experience it's doubful he could defeat Vader.
Given this was the power progression of the Chosen One, the guy who has had the largest number of midichlorians in his body ever, it would seem that this power progression speed would be a good max. It then stands to reason that if Yoda and Ben assumed Luke had the same amount of midichlorians as his father (maybe they did a test or something) that he would eventually progress at the same quickness or if given intense training at a faster rate. However, not that much faster. If we apply this and we seriously take these implications then we know Yoda and Ben's plan didn't make sense. If they reaslitically expected Luke to defeat the Sith his training should have started much earlier.
I know, I know you guys are going to say "but if they trained him it would cause ripples in the force and the empire would find them" which ok I understand but then if that's the case they should have thought of a new plan. Because realistically they were foolish to think that Luke could defeat the Sith with the amount of training they gave him. Besides this ripple theory hasn't ever been proven and there is actually evidence to the contrary. When Yoda trained Luke in ESB the Sith never sensed anything nor could they find Luke. The fear seemed unfounded.
Considering Luke's skills and power in ROTJ and what Yoda knew of the Emperor's power, they should have known that he didn't stand a chance against him. He probably didn't even stand a chance against Vader at full power. Yet they send him off telling him he was ready. Bullsh*t. They are basically sending him to his death.
They might as well have sent Mace's posse and expected them to do better. Fans will say that they were counting on Vader to turn and destroy the Emperor, but this isn't supported by what Yoda and Ben say. They say Vader is gone and that the Dark Side forever controls your destiny.In short, the PT completely destroys any validity that Ben and Yoda's plan could have had.
If they were really intent on destroying the Sith what they should have done was after Yoda had run away from defeat against the Emperor in Rots. He should have joined with Obi-Wan and then gone to try to assassinate the Sith again. Vader was severely weakened and the Emperor wasn't as strong as he would later be. Combined they could have produced a bigger threat to the Sith than Luke ever could at the time of Rotj (powerwise that is, no one counted on Luke's power of compassion).
In short, Yoda and Ben's plan doesn't make any sense at all.