Using the same gun all the time in FPP is wrong and confusing. Big guns claim respect, smaller ones are basic or light weapons. Besides, in FPP it's important to see what gun your enemy is carrying. That would be good in JJ2, too. Let's say you see somebody running straight at you with a Seeker Launcher. You're trapped in a corner. And then, all of sudden, he switches to Frostbiter because that previous gun was out of ammo...
Also, if all weapons fit into this one baby, why do we need to collect new Basters with different dot colors? I say - different weapons, new weapons, new working systems. Weapons in JJ2 are good for a platformer - but in FPP they need a lot of enhancement.