Effort has nothing to do with it. I don't see anything about effort in the FTC's definition of monopoly. [1]
"Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors."
"Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors."
[1] https://www.ftc.gov/advice-guidance/competition-guidance/gui...