Just because they resulted in a dead animal doesn't mean they performed well. Sierra bullets have produced some atrocious wounds on animals I have shot them with, even with somewhat big caliber, heavier bullets such as the .308" 180 GameKing, especially when impact velocity is high.
Slow them down, shoot them out of a .30-30 or something like that and they'll be fine I am sure, but they're not for me and my normal hunting rifles.
I have also found them to be like Nosler bullets, in that they're normally accurate out to X yards, then their accuracy goes to hell, I presume because their internal concentricity (or lack of) causes them to wobble like a Marine on liberty once they slow down to a certain point.
The 63 SMP is the sole exception for me, out of my .22 hi power. I believe it is a varminter bullet though, not a GameKing or Pro-Hunter and I sure as hell don't shoot it long range.
Having run thousands of Sierra bullets over a Juenke I completely disagree on concentricity being a Sierra problem. They simply are as good as they come. The old screw-machine Partitions are the only ones close.
Also, like any stabilization issue, it shows up from the start if it is there. Run a thousand Core-Lokts over the Juenke and watch how the tiny handful of perfect ones shoot compared to the average...