Yes.

: The Scattershot, Light Rifle, and Boltshot were unnecessary. The incinerator
: was fine as-is, since its shots behaved much differently from rockets and
: fuel rods.

No. Still a projectile weapon. Needs more to differentiate itself than submunitions.

: All the Promethean weapons could
: have also had a reload/overheat thing different from other weapons,
: perhaps having to hold the reload button down to charge them up. There was
: any of a number of ways they could have differentiated Promethean weapons
: from UNSC and Covenant weapons, but instead we got a Forerunner BR/DMR,
: Forerunner shotgun, Forerunner AR, etc.

A few reload mechanics off the top of my head:

1: Forerunner weapons draw power from the user's suit. Reloading a spent weapon depletes your shields, and the recharge rate is reduced to 25%.

2: Forerunner weapons draw power from the user's suit. Your shields cannot recharge while a Forerunner weapon is active, and you need to switch to a secondary weapon to recharge.

3: Forerunner weapons draw power from the user's suit, and are locked down to keep primitives like you from pulling guns off Warrior-Servant corpses. The Covenant have managed to jailbreak a few and use special energy cells to power the weapons. And since this batch of Covenant are actually pretty smart, the energy cells are rigged to explode when their armor detects a cessation of heartbeat and a sudden spike in blood pressure. In order to get reloads for a Forerunner weapon, you need to change up your tactics and perform assassinations.

4: Forerunner weapons draw power from the user's suit, and are locked down to keep primitives like you from pulling guns off Warrior-Servant corpses. The Covenant have managed to jailbreak a few and mounted energy broadcast systems on Engineer harnesses. Jailbroken Forerunner weapons recharge in the presence of an Engineer. Just don't get too close, or the blasted thing will try to 'repair' it and you'll get locked out.