If diving is your priority, you will have no problems filling 2 weeks with dives just in the Sinai, without even needing to go to the African side of Egypt (Cairo, Alexandria, Luxor etc.). Between Dahab and Sharm El Sheikh in the Sinai, that ought to cover 2 weeks pretty good. In the meantime between dive days, you could still do quadbiking, camel safaris (there are even camel safaris from Dahab to dive sites such as Ras Abu Galum or Gabr el bint), horseback riding etc. In Dahab, you can even spend 2-3 days picking up boardsailing/windsurfing which is second to diving as the watersport activity there. If you really want to go rustic Bedu style for a couple of days, Nuweiba is another option with half-decent diving (it's between Dahab and Taba). Would suggest that you miss Taba. Mediocre diving at best there relative to Dahab and Sharm. Unless you're flying into Taba (a real hole of an airport), and even then, it would probably better for you to fly into Sharm (SSH) which has more flights anyway than Taba. Moreover Dahab is nearer to Sharm than it is to Taba.

I haven't dived Hurghada, but I seriously doubt that it's better than Dahab and Sharm. In my incomplete and biased opinion, Red Sea diving is really about the east coast of Sinai from Dahab down south to Sharm and Ras Mohammed.