All above makes a lot of sense.
I do wonder why they didn't include the pistol as secondary. I know how much (many)people hate AR-only starts, but I always thought it was an attempt to force (maybe force isn't the right word, let's say encourage) a more mid-range fight off the start with some roles being further defined by who went to grab which weapons of spawn. When I first got a handle on it I thought of it in terms of the pre-match buy options of CS, but happening in-game (not an apt comparison, but hopefully you get my drift)
The idea of say Sandtrap, and seeing the other team but not being able to engage them seems like it could have that cool battle rush type feel (you know those scenes in movies where the two opposing forces rush toward each other and collide in a massive cluster of destruction and death). Though it never really worked out that way and after that first rush (which may or may not happen) it never really occurs again and you spend more time looking for the ammo you want instead of engaging the opponent. Which actually happens a lot in halo 4 if you are picking a less popular weapon and one that seems to run out of ammo quickly (thanks a lot, light rifle).
One reason I liked the idea of it was the calm before the storm, having the time to actually think about what was happening, which is actually why I'm not much a fan of instant respawn and sprint for some of the same reason. I'm fine with them, but think the game is better without. Part of the reason I always thought the 30 seconds of fun idea was so great was that it was broken up so you could enjoy those bits.