Don't be so sure about that. When you consider the approximate mechanical advantage between clutch pedal travel and release bearing travel is way over 10:1 it isn't hard to appreciate the axial load on the crank from clutch operation can be in the hundredS of pounds. The helix angle of a gear x the radius of rolling contact point x engine torque just can't produce any force of that magnitude. The reason cars with tiny thrust faces can get away with it is that the duration of the loading is fairly brief whereas a gear thrust or propeller thrust in nearly constant.My memory is of Tracy saying that those bearings only saw load in the car when the clutch pedal was depressed. Was a long time ago; could be defective memory. Certainly much less load than that imparted by the helical cut sun gear.