So, the thing is: the Yamahas are my least favorite recorders sound wise. Though at one point, I thought I liked the Ecodear (I thought it was quieter and more mellow – you described it as muffled, I believe), they sound more plastic to me than the Zen On and the Aulos.
I do believe the windway has a lot to do with it. My Dolmetsch (and Bakelite Schott) have a wider windway. The Dolmetsch has a clearer sound than any of them and doesn’t really sound like plastic. I know that it has a straight windway vs the curved windway – which, if I remember correctly, means I would not be able to do as much as far as adding more expression, etc to the sound.
Also, with the wider windway, I can push more air through it (which I am sure is not good technique). I don’t have as narrow a space to focus my air so I don’t have to control the air as much.
And too, ability is another huge factor. People who can play well can do a lot with almost any recorder.
Here is an interesting article with three professionals comparing the yamaha, zenon, and aulos: https://americanrecorder.org/docs/PlastRec0991.pdf