I always looked at the balance of Reach in terms of 'opportunity cost' and teamplay.
This kind of balance has always existed to a degree in Halo, thanks to the two-weapon system. Choosing one weapon or another intrinsically meant that you were losing the specific advantages of one weapon in favor of another, and that you would ideally change your tactics accordingly to ensure you could maximize the strengths of the weapon you took with you.
Now it applies not only to choosing weapons, but choosing HOW to use weapons. I can choose to use the DMR at shorter range by spamming the trigger - but the cost is the accuracy and reliability that the weapon affords when shot in proper cadence at medium range. I'm making the choice to trade the opportunity for a potentially faster kill, at the cost of accuracy.
Unfortunately the bloom isn't perfectly tuned for this at present - spamming the trigger is a little too effective for my tastes, albeit still less effective than using the weapon at it's intended range.
Likewise for the armor abilities. I typically start out matches using sprint. I make that choice knowing that by selecting sprint, I am unable to use armor lock, evade, holo, jetpack or any of the others. So I play the game accordingly, choosing my tactics in battle such that I maximize the advantages that Sprint provides. If I ever find myself saying 'Damn, I wish I had <insert any other AA> right about now', then I have failed to play to the strengths of my AA, or failed to stay away from situations that favor the opportunity cost.
Obviously, aside from opportunity cost, all the weapons and AAs have their own strengths and weaknesses for players to take into account. It's all well and good for somebody to use the Jetpack properly, but the thing is still slow, loud, and turns you into a sitting duck to teamshoot, so you better damn well pick your spots. No different for the shotgun. Feel free to run into the open and kill that dude with a close-range instakill, just realize that now you're pretty screwed if somebody with a DMR sees you from mid-range.
None of this works if you play the game and intend to try and take down three guys by yourself. But I've never really rushed into fire-fights like that. It seems as though Reach was built to reward teams that work together.