Without being defensive, I'm not totally inexperienced with larger, narrower boats.
The Zephyr did indeed edge well. Almost too well, and maybe that was the problem that you describe. I didn't have to muscle it to turn at all, just to stay straight, and there was NO wind or tide I was pushing against in that instance (closed canal system).
I was fully prepared for the initial stability to feel very different and tippy by comparison to my own boat. That wasn't what bothered me. What got me uncomfortable was the inescapable feeling that I couldn't keep the boat upright easily in the easiest conditions you can imagine. I didn't feel that I could take my hands off my paddle for a second to adjust anything, pull off gloves, take a picture or anything else one should be able to do. That is simply a highly discomfiting situation and didn't inspire confidence that it would change.
I'm on the borderline for 155 vs. 160 in the Zephyrs at 5'11" and 190 pounds. I can't use a really tight cockpit, as I'm recovering from hip surgery and getting in becomes a problem, so the 160, given long legs, hip comfort and shoe size seemed the logical choice, as the 155 (tested only on the ground for entry) felt too confining, while the 160 did not. When I adjusted all the fittings I got more control in the 160, but it never felt like enough. BTW, I don't like being shoehorned in for any length of time.
My prior brief tests on water of larger boats include: Alchemy 14L (delightful, quick and sufficiently stable, but very tight fit); Delsyk Nifty 430 (overall very comfortable and confidence inspiring, and stayed that way for 6 hours during lessons); 2 different Eddylines (all beautiful but tippier than I'd ever like); Looksha (felt like a barge, though stable); some others I cannot remember. They're all pretty much the same width at beam, though the Alchemy & Delsyk are only 14' long.
So I'm not fully convinced that it's simply that I'm unused to the larger, narrower boats.