That sounds right. I missed the part where you said it's a 3.5kW motor. Mine is 5.5kW, hence the confusion.
Even if the torque is enough for some steel milling, you also have to keep in mind that the bearings stiffness in these spindles is lower due to the special geometry to allow these high speeds.
Just for reference, a small benchtop mill with gearbox and a 1.1kW/4 poles async motor has about 100Nm at 100rpm.