Yeah that's about right, the axles are stronger as they are slightly larger, but that means that they can only fit smaller bearings in which makes them weaker in that respect. So with normal isis bb's it's a swings and roundabouts kinda thing. The isis bb's with external bearings (e.g. echo, raceface) manage to combine both strong axles and strong/larger bearings though, so if you were to get an isis bb I'd say go for one of them