I'm working from vague memory here, but I seem to recall from my distant past when I worked in camera stores where both Leica and Minolta lenses (for SLRs) were sold, that the story was that the guts of a number of zoom lenses were identical between the two brands, except for three critical issues:
1) the quality control specifications - Leicas were much more narrow;
2) the badging; and
3) the means with which the elements of each lens were affixed.
The latter criteria was similar, but not identical. Naturally, the Leica lenses had parts that were more precise, but only because they were made more precise in more labour intensive ways.
I bring this up to point out that it is probably possible to have two lenses manufactured with what appears to be the same design, using similar qualities of materials but still have two different results. This is because certain choices can be made - certain more labour intensive assembly procedures and narrower tolerances may be chosen which result, on a statistical probability of higher quality results. In addition, certain higher quality ancillary materials may be chosen that result in better ergonomics, and possibly longer life without adjustment or repair. Finally, and most importantly, if narrow tolerances are required, fewer lenses near or outside those tolerances make there way into the marketplace.
If one was able to to compare a large number of Leica and Minolta SLR lenses of that era of identical focal length range, it is likely that there would be some Minolta badged zoom lenses from that era that would be of higher optical quality than other Leica lenses of the same focal lengths. All things otherwise being equal, however, there would statistically be more Leica lenses that would surpass the Minolta versions, even if only marginally.
Matt