@zevvion: To be honest I kind of like that I have to think a bit about my weapon combinations in terms of which exotic I want for which mission. It limits it a bit but I don't think the combat would be as interesting if I could just blaze all three exotics all the time.
Many of the exotic weapons aren't that great though. I have several exotics and don't see the big deal. I'd rather use The Comedian over Invective, there are blue and purple handcannons I'd use over Thorn, which is pretty crappy due to the lack of impact and mag size. Using a heavy as your one exotic slot seems like a bad idea. Some exotics seem good like Pocket Infinity, but overall I'd rather have purple than yellow, since purple is just as good and quicker to upgrade.
Most Exotics are extremely good in a particular way, but they seem to have trade offs. For example, Ice Breaker does a ton of damage and regenerates ammo which is insane. But you can't actually reload the weapon, so in instances where you need more than 6 shots you'll have to take cover and regen ammo first. It can both be amazing or a pain to use depending on the situation.
I think it's dumb you can't equip more than one at a time. You can equip Legendaries all you want. Some of them are better than Exotics. I just don't see what the problem is; with the possible exception of the Crucible, but I don't see why you can't have different rulesets for PvP and PvE.
I just got the "Devil You Know" (a purple) and it's better than the two exotic handcannons I have (Thorn and Last Word). Invective would be better than The Comedian if the mag was slightly bigger and it didn't have a crazy reload time. The problem is that they're trying to balance PVE and PVP weapons at the same time. I'd be fine if exotics were badass, but couldn't go into PVP, or if going into crucible changed stats. No one really asked for versus, so nerfing weapons to please the side part of a campaign game is a bad idea IMO. That would be like Gears nerfing guns for versus when most people bought it for campaign and horde.