system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why is Palpatine desperate to get a powerful, young apprentice - first with Anakin, then with Luke?

The obvious answer is that "If I don't turn them to the Dark Side, then they will grow to become powerful enemies as Jedi". Which is fine, I get it. 

But, in a world where the Emperor wishes to set up his Rule of One, seeing himself as the culmination of the Sith, why does he NEED a powerful apprentice? 

When Vader became a cyborg, surely he was perfect for the Emperor. Still exceptionally powerful (at around 80% of the Emperor's power, or thereabouts) and fully under the thumb to do his bidding. He had no need, in the Rule of One, to have someone to teach all of the Sith secrets to. Just subordinates to exercise his will. 

And yet, at least in the old EU, the Emperor demonstrated nothing but disappointment that he was robbed of a powerful apprentice that 'could have been'. So much so that he kept trying to get him killed off. But a fully powered Vader may well have grown strong enough to defeat the Emperor, and therefore undo all the good work in setting up the Rule of One. 

With Luke, he finally saw the opportunity to get the Anakin he initially wanted. And as mentioned above, yes, if he didn't turn him, then he would've grown as a powerful Jedi. But then he still would've faced the issue of potentially being overthrown.

The need to search for a powerful apprentice falls in line with the Rule of Two, to ensure the progression in power of the Sith. But in a world where the Emperor intended to be the final master, why?
gpt
If using your power has a negative effect on you, better to have a flunky to run blocks for you.

Have the 2nd most powerful guy fight with the 3rd most powerful guy.

Then have the winner fight the next one.