You're right. I do associate "properly fitting" jackets to one that is "close to" the body type of the wearer usually. In my mind, a snug fitting suit works well with skinny people or muscular people with lower body fat percentage. Also there are some exceptions, e.g., someone with small shoulders would benefit from structured shoulders and perhaps an elongated shoulder. But I don't think a sack suit would work on a really skinny person. E.g., a sack suit would probably not look all that great on Neil Patrick Harris.
Those Formosa jackets were not tailored to fit TweedyProf. Maybe after it goes to the tailor, it will look the jeffreyd jacket, but to my eye, the style didn't seem right. Also, if he was wearing suit pants or pants tailored to match that jacket, it would have looked perfect.
No, they weren't tailored to fit me, but as I said, the 46 was tighter on me than the Jort 48. Greg "broke" it in a bit, which would happen with normal wear (a bit of pulling and stretching) and then it settled in nicely. But I'm not seeing the issues you are pointing out as so starkly different between the jackets I'm wearing (Jort vs the Formosa below).
If you look closely, jeffreyd's chest is actually drapier than the Formosa I'm wearing above. But the extension is about the same. Look from the shoulder curve on the the right arm side (notice more drape in J's coat though his waist is more suppressed). If anything the Formosa on me has a more trim appearance above the button point (waist aside). The lapels are wider and perhaps that's throwing things off for you?
I actually worry that the size I was wearing in that Formosa pic is too small as it is rather trim in the chest. Here's the back of the Formosa (rumpled because I had to raise an arm to take the pic). Arms down, it was quite clean and not really different from the Jort. I wouldn't call the back drapey
Anyway, I think it's good to articulate clearly, as you have, your preferences. I tell my students, writing is the key to clarity of thought. That and coffee.