in a way i think the complexity is what makes it a good beginners deck...at least from my perspective of learning things.
to me, in any area of life, if you start off learning on something really basic, you might learn faster, but what you learn will be limited. As soon as you move onto something different, likely more difficult, you'll have to re-learn/spend the time improving etc just to be competant. If on the other hand you learn on something much more difficult, when you move onto something else, its likely to be the same or easier, so you'll be good right away.
like, when i learned to rollerblade about two years back, i learned on skates that went very fast, and i learned by skating in streets that are very hilly and full of pot holes, gravel, sand etc. It probably took longer, and I fell a bunch of times, almost ran into cars, etc etc. But once i got good...I can skate anywhere, basically. When I went to Boston, skating in the streets there was quite easy, not a problem at all by comparison. I can skate at night, on slick ground, and not be bothered, in other skates too if I need, etc.
Same with tarot, it would seem to be. If you start with RWS, not only are you already familiar with the system that most books are based on and which a lot of decks follow, but if you actually really familiarize yourself with the more dense imagery/symbology etc, other decks will either be familiar, or even simplified...whereas if you start off with a simple fluffy deck, later on when you move to a more complex one, move to the RWS, whatever, you're just going to have to re-learn, feel like wtf why is nothing familiar, etc?