Yeah, but destiny can't/won't be competitive and balancing is a big concern. Also, as other mentined, req packs will provide you those other weapons that have different features/skins. You'll also have other items to aquire other than weapons to customize your play. Sure there are only about hundreds of variantions at launch but i expect them to increase that in the following months after it's release.
A little comparison list:
Destiny (Halo)
Hand-Cannon/Sidearm (Pistol/Magnum)
Auto-Rifle (AR/Storm Rifle)
Pulse-Rifle (BR)
Scout-Rifle (DMR/Carbine)
Shotgun (Shotgun)
Sniper (Sniper)
Heavy Machine-Gun (SAW)
Power based gernade (Multiple gernade types)
Rocket Launcher (Rocket Launcher/Hydra)
Fusion Rifle Focus Rifle
Sword (Energy Sword)
(Needler-Homing bullets)
(Plasma Pistol Secondary- 1 shot sheild emp)
(Plasma Caster/gernade launcher)
(SMG)
(Fuel Rod Cannons)
(Spartan Laser)
(Rail Gun)
and more promethian weapons i can't think of right now.
Now i think about it some more, there isn't really much of a difference in the combo you metioned. Actually it seems like Halo has more categories of weapons to choose from.
If you are looking at the difference in how the Auto/Precision/Heavy weapons shoot; Like colors n stuff, then maybe you won't be pleased because bungie has that locked down and doubt any shooter can top that visual flair they posess. (except insomniac - love you sunset overdrive)
Anyway, that's what i think about when you said they need to mix it up a little. ^_^