I agree. It's not just the bearings (impportant though they are). The S7 has:
Better tailstock
Leadscrew handwheel
Longer cross-slide
Vastly improved topslide mounting
Countershaft clutch
….and probably other things I've forgotten. The ML7R has some, but not all, of these improvements. As for gearboxes, I have the impression (though I've not done a careful check) that the difference in price between S7 and S7B is less than the cost of an add-on gearbox. I certainly wouldn't want to go back to achangewheel machine again, even though you do occasionally have to use changewheels for unusual jobs.
David