You're precisely right. And this is why Ambush Grid is great in theory, but worthless in reality. Lets take your average OP Plat gun in the Rozerad or Hurricane or Silhesh, Ambush Grid offers half a bullet bonus, from a gun that takes a clip or two to drop the biggest enemies, it doesn't really achieve anything.
And that's why I leave it at 1.
Same. Still get all the utility, with none of the cost, letting you max everything else and being better all-round. MAYBE a Black Widow Huntress would be better with Ambush Grid, but that's an entirely different discussion.