The Thoth is a complex deck because Crowley's was a complex mind and Lady Harris's art one of complex imagery. You cannot fully understand what Crowley intended by reading works that reduce his vision to the level of the "average reader." Say what you want about him, but Crowley was not "average". You actually do have to learn about all those things Crowley knew in order to understand and appreciate his Tarot, just as you have to know many different things about the world of Renaissance Italy in order to understand and appreciate the Sistine Chapel. The Thoth deck was not intended for the "average reader" any more than quantum mechanics was intended for the average plumber.
If you want to learn more about the relationship between the Qabalah and Tarot get a copy of Robert Wang's
The Qabalistic Tarot from
http://www.marcusaureliuspress.com/ for an excellent and detailed overview, and continue to study -
study - Crowley's book. He's not an easy read because he's not writing for "average readers," he's writing for the handful who will have the energy and motivation to do the kind of work he did in order to write his book. If you're not willing to do that - and there's no shame in that - then just forget about it. There's no reason to put a lot of energy into studying something that doesn't interest you. But reading popularizers who've done all the research and then reduced it to a Dick & Jane primer for a quick buck is a waste of both your time and your money.