If I still lived in the USA, I would do this. However, since moving to Austria, I've found that by far the most important thing here is academic credentials. They're still really old school that way. I've watched less experienced, dimmer candidates get picked because they had a better title.

Without more letters next to your name, you hit a wall. Simple as that.

Is cracking the coding interview useful for learning comp sci topics or is it more of a cramming tool for interviews at big tech companies?

Yes. Do this first and do the online course while working.