Yes I agree completely that elementary concepts and techniques of arithmetic (the concepts behind which may not even be so elementary) are essential and must be

Yes I agree completely that elementary concepts and techniques of arithmetic (the concepts behind which may not even be so elementary) are essential and must be understood by any math student, but I distinguish strongly between learning said concepts/techniques and repeating them ad nauseam in frivolous repetitive exercise that demand no originality in reasoning whatsoever. I love math and would be considered by most to be a decent student, but just looking at those problems gives me a headache, and never have I encountered a circumstance in which carrying out those types of calculations by hand was remotely necessary. I will note that the memorization quote is particularly true with more abstract topics where definitions are crucial to understanding ideas and writing proofs.