Henry Scherer wrote that the quality of Soviet lenses varied greatly: one might come across some very good lenses, but also absolute rubbish. It is possible that the assembly process, particularly for the Sonnar lenses, was so complex that it was only mastered to a sufficiently high standard in Jena and Oberkochen.
I've not been inside as many Soviet lenses as Brian Sweeney, but I have tinkered with enough to make me think three factors lead to this assessment:
1) some Soviet factories and some Soviet eras were definitely worse than others. Brian said that Valdai-made Jupiter 3s were noticeably worse than KMZ-made ones; I'd be inclined to agree. As with any product made in multiple locations, even today, not every assembly line was made equal. This is less of an issue with Contax mount ones than the FED/Zorki mount ones, but it's still something to consider.
2) Soviet lenses have often been mistreated. Lots of them have been tinkered with by people who really don't know what they're doing (which is related to
@TenEleven's post above), as they're cheap and considered not worth sending out to professionals. There's also a lot that have been cobbled together out of parts. This leads to inconsistent "quality", but doesn't necessarily reflect how the lenses left the factory originally.
3) Good ol' McCarthyism. Henry was very good at repairing Contaxes, but his website had some...
unusual sections if you did some digging. It wouldn't surprise me if he was one of the many, many Americans who had internalised the Cold War anti-Soviet propaganda enough to immediately discard everything Soviet-made as low quality... just as we see other Americans of similar age deride the lenses coming out of China today. I've had more problems with German- and Japanese-made lenses than I have Soviet ones, but I think for a lot of folks, it's easier to give those a "pass" than it is things out of the former Soviet Union, and that's more to do with politics and ideology than anything else.
For context, based on my small collection of Contax-mount lenses, the only lens I've ever had a real problem with was a post-war (West German) Sonnar which is so far out of spec it's impossible to get accurate focus, but I've never had a Soviet-made Contax lens of any design that didn't work and produce good images straight out of the gate. As a special bonus, because the Contax mount is so comparatively obscure, they tend to be butchered a lot less than the FED and Zorki equivalents, which have often been tinkered with to "fix" them for use on a Leica. And they're often cheaper, too!
As a result, I stopped recommending FEDs and Zorkis to rangefinder beginners years ago. The Kiev system is a much better deal - and via Amedeo adapters, you can actually use the lenses on other bodies further down the line, if you see fit to do so.