I don't think it's one or the other. I struggled a lot through differential equations because I didn't have good memorization skills. Had I memorized all of the formula it would have helped me get more out of doing the problems.

It's like learning Spanish. If you memorize a bunch of words you won't be able to speak Spanish. But if you have a bunch of Spanish words memorized than you'll get a lot more out of reading/listening/ trying to speak Spanish than if you don't.

And memorization is usually a far less taxing activity that you can do on your phone when waiting in line or using the bathroom.