More likely than not, those are constant torque spindles which are rated at 24000 RPM. Assuming they’re properly rated, that’s 2.8, 5.28, and 7.75 in-lbf for the 800, 1500, and 2200 Watt spindles respectively. Those torques would generate 22.4, 42.2, and 62 lbf respectively with a 1/4" cutter diameter (half that with a 1/2" cutter). The stepper motors on the Shapeoko can only provide ~18 lbf before they slip (lose steps). Although using a 1/2" diameter router bit with a 1/4" shank wouldn’t cause the steppers to slip, the 11 lbf would probably be too much for Shapeokos (regardless of the spindle size).
High spindle torques are counterproductive, but high spindle speeds (RPMs) aren’t. Running at the maximum spindle speed is necessary to get the most power out of the spindles (to maximize material removal rate (MMR)) as well as minimize cutting forces (at all MMRs). The larger the spindle, the better balanced it’s rotor needs to be to keep vibrations in check at high speeds. (Is that why you seem reluctant to run your 2.2kW HY at 24000RPM?) IMO this is a case where “bigger isn’t better”. Maybe someone like @wb9tpg would be willing to weigh in with his 800W spindle experiences.