Is this poor manufacturing

[Brion Toss]

Hello,
Sound suggestions above. I'll just add that, regardless of how strong these turnbuckles rate -- or even how strong they actually are -- there is not excuse for this kind of poor quality control. Send 'em back.
As far as the difference in load ratings, I'm curious: did you compare break strengths, or just rated load? Different manufacturers will use different numbers, and the less scrupulous will inflate their rated loads, right up to the yield strength of the material, instead of using a sane factor of safety.
As for mentioning the brand, please feel free! We have no advertisers to offend here, and in any event we all have a duty to wake up manufacturers, and to protect one another from the sleeping ones.
Fair leads,
Brion Toss