I understand that he is trying to give us a comprehensive understanding of how to work through a question but I would love to see a condensed way of getting to the right answer, perhaps so that we are able to see how to arrive at the correct answer in the limited amount of time we will have on test day.

What you do is pick ther best alternate option given the premises in the stimulus. It is "weakening" the argument because it is giving a strong alternate hypothesis

This is how I think about it:

"No student is chosen for Gryffindor unless they exhibit bravery" essentially means that bravery is NECESSARY but it isn't SUFFICIENT to get into Gryffindor. The second sentence, "therefore, if a student exhibits bravery, they will be sorted to Gryffindor" assumes that bravery is the ONLY trait required to get into Gryffindor.

I genuinely feel like using lawgic is making things more complicated for me. I understand what the sentences and conditions are stating and then I look at the answer and it confuses me.

They are the same! Major premise = sub-conclusion. It's a claim that both gives and recieves support.