people got fed up to what you called "getting mowed down" they now know how to counter.
So nothing happened to the sentry gun.
players are changing their loadouts.
Your question does not make sense... It is not an issue.. you seem to be complaining that people evolve.
Hhaha! Made me chuckle!
I always use Sentry's, sometimes they do well, sometimes they last 10 seconds. Taking the rough with the smooth is what CoD is all about.
A lot of people switch to a class to take something out. My "anti-streak" class has Tactician with two EMP 'nades and two Black Hat with the FHJ-18. Some people even run a class like that constantly.
I can see where you're coming from though... It's happy days when the enemy won't bother doing anything to your Sentry or Chopper, but if you're having a full night of launchers and EMP grenades it gets annoying.
If you have a friend or two, you can use a Sentry Gun, then have 1 or 2 others put down Trophy Systems by it, lol.
that's a good point, i was gonna mention that too about the trophies!
Placement is definitely the key along with timing. I find that putting up a sentry in a corner near a spawn point or somewhere away from the action will definitely last a lot longer and will get more kills from players not aware that it's there and they will usually spawn at the other end of the map to assure they have a much more difficult time getting back.
You can also choose to control the sentry if the action begins to move back in that direction. And by action i'm referring to groups of mass killings.
I just love it when people put that crap of a kill streak up, it means more points for me and my kill streaks. What i love about the emp nade is you dont have to throw it right next to something for it to do work, just close.