Jealous, are you?
If AIU was that good, we'd see her almost in every single PUG lobby. Which is not the case. She's not that good.
P. S. Piranha GI should get me through my bronze solo challenge, just completed the second attempt pretty easily 
Maybe you weren't playing when Reckoning went live, there was an AIU in every pug, back when repair matrix was retardedly overpowered.
Then bioware nerfed it, and the simultaneous deluge of tears from the scrubs and the laughter from the non-scrubs was truly a great moment in ME3's chequered history.
As for AIU being the "best" shotgun platform, I'll quote a taunt from UT: "NOT EVEN CLOSE!"
Classes with accuracy bonuses played by individuals who can aim will always out damage an AIU, as they are not hamstrung by needing to be point blank with a raider, as an example.