I've abandoned many decks almost completely because I made too complex cards.

Make the cards simple and combat interference. That doesn't mean you can't learn complex concepts. Now that I've got it right, I can go through hundreds of reviews per day if I've fallen behind a bit, and don't find it exhausting. If I manage to review every day, it's because I'm doing it first in the morning.

I use a plugin/option to make the answer show automatically after 6 seconds, so it's easy to spot cards that are formatted badly or cause interference, and take too much time.