In books like Stewart, staring at a theorem until you can write it's proof should trivialize most problems in the book.

If a method for solving a particular problem is too difficult for you maybe consider researching and/or inventing some new method to solve these problem. People created these methods in the first place because earlier methods were too tricky

Or just focus on work that doesn't require hundreds of hours to gain proficiency. As long as you have time every day to stop, think, and come up with an idea that solves a problem you won't become intellectually unfit.

Most math majors I knew hated the standard calculus courses, for precisely this reason. It's taught this way because they're targeting engineers and some hard sciences (physics).

The reason is that for many of those majors (EE, physics), you will take courses where doing calculus is your daily bread and butter. You need to be as adept at it as algebra. Over 50% of HW problems in those courses will involve calculus. They really don't want students who understand circuits but can't do anything useful because they stumble on calculus.

They are the largest "customers" of the math department, so the department caters to them.

Do all the homework problems check the answer in the back of the book. You’ll make it.

It schedules everything for you including the review so you just have to keep showing up to do the work.

Even as little as 30 minutes per day done consistently for months will have you make tremendous progress.

And once you master multivariable calculus, fields like probability and machine learning will be unlocked for you.

Most of the time I've found that the deeper I plunge into abstraction in math I get rewarded with an extremely elegant formalism. Its like upgrading your weapon in dark souls, the early game enemies get one-shotted when you go back.