Regarding the W series, I'd agree that there is definitely variation from one model to the next, but I wouldn't say they're completely devoid of similarities. They almost all share a certain timbrel coloration in the midrange which has come to be identified explicitly with Audio-Technica and gives them their reputation for being one of the best headphone series for vocals. Also with the exception of the W11JPN and W1000X, I'd say they all have a somewhat similar tonal balance (tight down below, bright up top).
For instance the W5000 and W3000ANV sound more alike than dissimilar in my opinion, with the former being the airier and brighter take and the latter being a more solid and balanced take on the same type of sound. The "Limited" models (W10LTD, W11R) tend to have a more neutral overall balance, with relatively less of that distinctive timbrel coloration in the mids.
This has been my experience, at least. Currently I'm only lacking the W2002, so it gives me a chance to A/B them.