Depends on one's background, really.

I understood some videos really well on the first watching, but some videos on the same technical level were like- "what?... Ooh, maybe that's okay... Oh... Yeah". Total discomfort.

It's the areas of Math where you already have decent groundings, you will find that you can take more with you from 3b1b.

Same with Feynman's Lectures. If you are a smart person but no formal background in Physics, they are fun, sure. But you read the same lectures as a Physics undegrad in your Junior or Senior year, your 'return' from reading those lectures goes up five-fold.