That is how people learn how to pass tests instead of learning the material. Passing tests is important in college, but if you want to learn on your own it doesn't matter.
Yes, but I'd argue that the path you took was a very suboptimal path to reach the same understanding since you almost surely didn't reach it. So now you'd have to redo almost everything in order to reach the same goal making it a very huge waste of time. Of course I cannot be sure of that, but I have seen so many people who learned the way you did and they had really poor understanding. In my experience only the people who try to challenge themselves actually gets there.
Passing math classes requires almost no understanding at all btw, even getting good grades in them doesn't.
How about look at the solution, understand the parts. Solve the problem. Revisit, revisit, revisit.
This helped me breeze through engineering and also helped me professionally.