Not going to bother with the weight question anymore because we're just going in circles, and my experience from having been a 300+ pound rider is that it's a lot worse than you say--but he also may be too tall for the WM bike.

In the $250-400 price range, there are lots of hybrids that are all rigid frames. I just bought my youngest son a Raleigh Detour 2 on sale, and he loves it. It's labeled as a "comfort bike", but he finds it great for riding around the Boston area at a pretty good clip. Having just shopped for bikes at this price range, I can say with some confidence that your characterization of the available bike store options is just wrong, and if that's all you're seeing, try a different bike shop.

No suspension features, they definitely suck at that price range. Worst one, btw, is imo the bouncing seat post--those things really don't help anything, and generally have a really hard time dealing with a heavy rider.