Solving math by "subject" or "theme" unit is beneficial to brush up

There about 850 math problems, and I solved all of them except for "advanced math" chapter. As a result, my first quant score on November became nearly 70th percentile, not bad for a guy like me who had been apart from math for 16 years. I will keep studying with equanimity and confidence thanks to the book.
A lot of problems, 850, were enough for me to familiarize to each theme like Algebra, Geometry, Standard deviation, and so on, in comparison with ETS’s official guides having up to only 300 problems.
"Learning per section" cannot be attained by solving OGs. This is true that OGs’ are the most authentic, but we the beginner gets lost easily, and get lost. I got lost by only using when using "only" OGs in math problem sets.
A caveat is that some problems of the book are straightforward, if not easy or instructive, and this is not the way actual GRE questions take.
Again, familiarizing myself with each math topics with a plethora of