Aluminum blocks are fine. 20wt oil is fine for non-turbo cars that call for it. Turbos are fine. I've seen turbochargers outlast every other component on the engine. I've seen many, many cars with all of these components do just fine to almost 200k miles. I personally just sold a car with the above-mentioned components that had 179k on it. Just keep them properly maintained.
However, I have seen this issue before with GM back in the early 1980's on big block engines. Undersized rod journals and/or soft crank/rod bearings.
The rod/crank tolerance is about as critical as it gets in an internal combustion engine.
A couple of thousandths would all it would take I imagine.
Or, like you said, substandard materials.