10 HP single phase motor serving exhaust fan having trouble starting.

[kwired]

Actually, I think that in this case no "drive"' means no variable frequency drive (VFD) which could make starting less stressful on the motor and also result is a lower startup surge current.
Since the motor is single phase and the wire runs directly from the starter to the motor on the roof, there does not appear to be an unnoticed VFD in the picture.
We are also assuming (with justification) that the starter and motor combination do not implement wye-delta switching, high-low voltage tap changing or other specialized ways of reducing starting current at the expense of starting torque.

The main justification is the fact it is a single phase motor. If it has a centrifugal switch to disengage starting capacitors which is usually the case, you can not run at reduced speeds, or at least below 70-80% or so or the start capacitors are still going to be in the circuit and they are not built/sized for that kind of duration of use in this application. Even if they were, the motor would draw excessive current while they are in circuit when not needed. If OP's motor overload would hold long enough this motor would start and run successfully, but unless designed for it, would suffer over time from excessive heating during starting, and the more starts the shorter the life expectancy of the motor may be.