On the meanings of INTONE
Solution 1:
“Am I the only one ... ?” I take to be an unanswerable rhetorical question.
The definitions you quote seem to be consistent if we understand “rising and falling” in the sense I believe it to be intended: repeatedly rising and falling. {Up, down, up, down, up, down, ...} rather than simply {up, down, finish}. The variation from up to down may be only small, as in (for example)
Intone = Say or recite with little rise and fall of the pitch of the voice.
Lexico