This is an erroneous statement and is of no help to anyone. No different than me saying there is a big midbass suck-out with UE900 making it cold and too analytical.
It still comes down to tastes and preferences. I don't think Westone spent 1000's of hours of engineering on W4 to purposely screw it up. You don't think they know what they're doing?
Again, W3 midbass could surely be considered overdone by the majority but the midbass of W4 provides warmth making it soothing and engaging, purposely shying away from a colder more analytical sound of a W2 type sound sig.
The brief time I had UE900 I really liked it but didn't have enough time with it to say it trumps W4.