Shame on you, trying to apply logic to language!
I don't ever use the term "conventional gear," precisely because it is not descriptive, and thus ambiguous.
I use "tail-wheel" and "nose-wheel," or "tail-dragger" and "tricycle" - because they not only differentiate, but describe the difference.
And they are more efficient. My father, an engineer
and English professor and writing instructor, always said "Never use a long latinate word when a short anglo-saxon word will do the job."
If one goes by historical precedence for "convention", the Wright Flyer used skids. So really, the only "conventional-undercarriage" aircraft flying today are mostly small helicopters.