To add a different but orthogonal perspective to this:

My higher-level math courses were pure mathematics courses, and we pretty much always used Springer textbooks, which were only a few hundred pages long and the size of a normal paperback (i.e., not the size of, say, CLRS). When we didn't use Springer textbooks, we used other textbooks similar in size and length (e.g., [0]). I found these textbooks to be completely manageable to read as a student, and they were the best textbook-related learning experiences of my undergraduate years.

[0] https://www.amazon.com/Introduction-Galois-Correspondence-Ma...