The BBOS was not designed to be a responsive, touch-screen OS. It had its root in pagers (hence the jankiness). Thru the grapevines what I heard was that the OS team said 'we can duplicate iOS' functionality with the old OS in this amount of time.' and the higher ups rolled with it.
By the time Storm 2 was released, everyone realized that you can only put lip balm on a pig for so long. Hence QNX, the 'pathfinder' Playbook, and Flash as GUI API (gawd that was a rollercoaster experience. I thought it was a deathmarch and didn't think we'd actually manage to ship it.)
I don't have any specific insight into the Wifi stack but most BBs up to that point have in-house designed cellular modems.
As for talent wise, shrug. You can't blame people for preferring Cupertino over Waterloo-Kitchener. Although I would say that over 1/5 of the employees at RIM's campus were co-op students.
I also never saw anyone do significant overtime.