I'm honestly not really comfortable expounding on the differences between them yet. My HA-300 was outta commission while my WE tubes were sent back and I'm just now finally getting back into it. But I won't let that stop me
The Stratus, to me, is like a grand concert hall. The mids come through so clearly across that wide open stage and it leans warm, but it's not syrupy or wet. It's surprisingly tight, just not dry. When I compare it to my Glenn OTL, the Stratus sometimes spreads the music out so well and uniformly that the Glenn might come across more 'fun' or focused on slam and dynamics, while the Stratus just plays it all so effortlessly well. The Cayin is warmer and wetter to me (keep in the WE's have less than 100 hours) but not slow or syrupy at all, and it emphasizes the lower kids and bass a little more than the more even-handed Stratus. Cayin has a little more weight to it, big slam but not boosted slam, which the Glenn can sometimes feel like.
To make a ridiculous analogy, the Stratus is like smooth, creamy peanut butter while the Cayin is crunchy peanut butter. Still buttery smooth but with some extra oomph in the lower registers. Heavier and weightier while the Stratus flies like an agile angel.
To your analogy, if you had to compare the Stratus and the Cayin, yes - the Cayin is thicker and wetter and has more resonance, but I would never in a million years call the HA300b thick or wet, it's just in comparison to the Stratus. I also don't think that HA-300b rolls anything off up top, but when heard in its entirety the zing and tizzle is couched within that lower mid-thickness. It's there when you search for it, but it's not as apparent as on the Stratus. I was just listening to Frank Black's Headache and on the Stratus I would get some of that sharpness come through, whereas on the Cayin that detail up top was a little tamed by the thickness below.