Is this a thread about ammo powers or on whether the Soldier class is interesting or not, because the discussion is not quite the same.
Ammo powers could logically be used by any class as well as many of other abilities that are restricted to other classes. You can form theories about why it does or doesn't make sense for an entire month now, I don't see why it really matters.
If the ammo powers exclusivity to combat classes terribly bothers your sense of credibility of the ME universe that's one thing; if you're concerned about the gameplay itself that's another. I don't see how the former subject could be used to counter-argue the latter.
If we put ammo aside for a moment, if you give the Soldier a few new abilities that would behave as counterparts of current biotic/tech powers, I don't see how the class gets any more interesting as a whole or how the gameplay is improved; all you do is create a class that only very slightly differs from others and plays almost the same way.
The soldier does have its own unique abilities, just because you can't bind it to a number doesn't mean it's not there.
First of all the Soldier receive time dilation when sprinting which slows down the entire world.
Secondly you get access to the most guns which allows you to adapt to the situation and change your fighting style. Although you don't get a direct effect like using power X to get Y damage from Z, it adds flexibility that other classes lack, and the ability to switch to your SMG is not the same as switching to your Assault or Sinper Rifle.
Thirdly the ability to change ammo powers according to the situation should keep you busy juggling between them.
The idea is good, the execution is bad.
- There isn't a real incentive to use Shotguns or Pistol when you can use your Assault Rifle and Sniper Rifle.
- ARush is so powerful and Concussive Shot so useless that a Soldier ends up only using ARush and the bonus power. (From what I've seen in ME3 this has been addressed.)
- People don't really try new playstyles with the Soldier because it's so convenient to hang back in cover with your Rifle and spam ARush, something that a Vanguard can't do very well.
- Ammo powers don't offer a real bonus against different types of enemies and are clumsy to change, which makes it better to just use ARush even at that 1.5 seconds it takes to recharge, and players usually end up applying one ammo power at the start of the mission and forget about it.
Another thing I'd like to add is that the Soldier can be as interesting as you play it. It's very easy to take the Mattock and cut through enemies like butter with ARush and it could get repetitive and dull, but you don't have to play like that. Take a shotgun and try to go against suicidal odds and see what you can do.