You asked about how to best learn frameworks - great question, one that applicants often ask themselves.
When I was in your shoes, I also tried to learn a ton of frameworks ('Case in Point' from Marc Consentino anyone?). Ultimately, like you, I found that they were often confusing and didn't necessarily apply to the case I had to do. Worse, I found learning these frameworks a terrible use of my time. What does a framework really have to do? Basically, 3 things:
First, be MECE (Mutually Exclusive, Collectively Exhaustive); Second, help you go through the case in a structure and methodical way to not only allow you find the best answer; Third, convince your interviewer that your success is repeatable, and that you will crack this case and the next and the next.
Back when I was prepping for my BCG interview, I ended up falling back on just two frameworks, which I'd then tweak to fit the actual case: First, a version of the profitability model (Profit = Revenue - Cost, and Revenue = Price x Quantity); Second, a basic version of (Product, Price, Client, Competition, Company). Are these 2 frameworks optimal in every instance? No, they are not. Did they do the trick? I have used them in the 10+ practice cases with former BCGers, as well as in my 5 BCG cases... and I got in, so there's that :) I would even argue that every case can be solved by using either or both of these frameworks. Learn them, keep them in your back-pocket and be ready to use them. If you find a better one, great! But I'd rather you started with an "ok" framework and focused on solving the problem than spending 30 seconds at the beginning of the case to find the "perfect" framework, failed, and found yourself having to think on the fly as your start the solving process. At the end of the day though, remember a framework is just a tool. Good luck!