I had the same problem. My first and for some time only deck was the Thoth, then I bought Cosmic and Haindl, both closer to Thoth than RWS.... and it took some time to get used to my first RWS "clone", the Morgan Greer.
Maybe Wen's book is too much information? Maybe a book like 78 Degrees of Wisdom or a Barbara Moore or Andrea Green book is better, or Huggens 101? A book that focuses on card meanings and doesn't address so many issues like Wen's book.
Try to approach the RWS totally different, don't compare.
Can I use a personal comparison? I learned many years ago to touchtype. I can type fast and without looking at the keyboard in 3 languages. One of them is Hebrew which has a completely different keyboard. I can switch NOW my keyboard and start writing Hebrew. But don't ask me on which key is letter mem or nun! I couldn't tell you which letters share a keyboard. I can only USE the keyboard, but I switch into a totally different mode when I change between languages and alphabets.
And that's IMO what you have to do to read RWS successfully. Rely on the things you know: astrological and elemental associations, core meanings of the trumps (they're much closer than the minors), colour symbolism, general knowledge about mythological and allegorical figures and symbols.
And then use the narrative structure of the RWS. Where are persons looking at, what patterns can you see, is there a flow from card to card or not etc. It's much easier to start with the RWS because it's like describing a word of art. Your first entrance question is not "what do I KNOW?" but "what do I SEE?" Men or women or children, animals, symbols, time of the year? Start by describing what you actually see, it really helps. The figures seem to act out scenes - what scenes are they? Sometimes, the figures really seem to speak to us or each other.
I find that I get on best when I simply put on my RWS hat and take off my Thoth hat. The same is true for other decks, too. I work with the deck that I see in front of me. I don't use RWS or Thoth interpretations for decks that work differently. I know others that do; for me, that would be too confusing.