What I was thinking was that he didn't like the Rockhopper, which does have quite an aggressive riding position. Fast bike, if you like that sort of thing, but I figured if he didn't like that he's probably going to like the Genesis more.
I agree that comfort, as far as posture is concerned is much more about geometry. One of the things that attracted me to the Genesis bikes is that all the MTBs have the same geometry. The Core 20 for instance has exactly the same components and geometry as the Altitude 00 but on an aluminium frame. It was actually the Core I looked at first. In fact that would be a better match for the Rockhopper, it's exactly the same price.
Talking of young people, years ago I was talking to a guy in the shop where I bought my Hardrock about the fact I'd never felt the geometry was right. He said 'basically, it's because Specialized set them up for teenagers.' He said that it was mostly teenagers who buy them, or get them bought for them more like, so that's who Specialized target.
Whether I agree with that I don't know. I've tried the Rockhopper and the things I don't like about the Hardrock are pressent in the Rockhopper too. I changed the stem, bars and saddle on the Hardrock. I've not had to change anything on the Altitude.