no one's talking about rushing through anything and lacking understanding for fucks sake
this stuff is not that difficult
do you know how many hours there are in a day?
also, i'm not interested in number theory but i'm sure simple diophantine equations are no problem.
we waste a lot of time making foundations for things which are completely intuitive perfectly concrete. sure, it's good to spend time doing that for earlier topics, but not every single person is doing that for their first time in college. some of us cared enough to learn a proof based linear algebra sequence in high school because we thought it was fun. some of us also learned some basic analysis because we wanted to know why calculus worked so well. again, not every high school class goes "the integral is a limit of sums, okay now let's just take antiderivatives," some of us actually decided to learn why riemann integration works.
this isn't that complicated. and once you've seen the absolute basics in detail, you never need to see something in detail again unless you want to work really closely with it - sure, i get it, a group is like this. i remember how i proved things for vector spaces and for the integers, and i can just do those things. alright! i don't have to do 70 computational problems, i can get to proving identities, lemmas, propositions, and then some bigger theorems.
not everyone needs 4 months of slaving over an introductory textbook to get what's going on with the very introductory material in a very intuitive field of mathematics. measure theory is intuitive, and sure you spend some time on the few unintuitive parts. same for most of this stuff.
i'm not saying homology or integration of forms or gauss-bonnet or hahn banach separation theorem are intuitive or easy. i'm saying that someone with even a modicum of experience can get the intuitive stuff quickly and "master the content" on the interesting non-trivial things.
practice is practice.