I guess it is something we are all trying to get to grips with.
A lens with very good central performance tends to look good on APS-C, however, edge performance tends to become significant with full frame.
One lens that really surprised me was the cheap ultra compact 28-80 3.5-5.6. You really really really do not want to take pictures at 80mm f5.6.
Stop it down to F8 or 11 and it is spectacular. Shooting on 35mm Ilford delta 100 is as good a test as any.
But I digress.
There has always been variability with lenses. My "good" 24 mm may be better than your 20mm but the converse may just as well be true. For example our friend at Artaphot who has done many tests with both the A700 and A900 has a very disappointing 24mm. He shows the 20mm to be much better. MJ Hohner in his test of the 17-25G vs primes shows the opposite. My 24mm is really good even at f2.8 across the field. First generation version, "refurbished" from Minolta USA.
It does not help that an 8x10 inch print was regarded as an "enlargement" in the good old days and now everything has to be sharp at 200%.
One interesting thing is that a lot of the older reviews I have show the 20 mm as being mediocre. (Do not feel bad, the Canon and Nikon equivalents were also just as bad) Later reviews show it as relatively good. Did something change in the late 1990s? At least it is better than the 20mm F2.8 MD, which had terrible vignetting problems.
I notice some general trends in most reviews:
The 24 is generally good.
The 28 f2.0 is much better than the f2.8 which is in the "why bother"class
The 35mm f2.0 is a great little lens and better generally than the f1.4. (price/performance)
Of the 50s, the 1.4 is generally better than the 1.7. the f2.8 Macro is best except for a "sensor flare" issue on some older lenses.
Pop Photo called the 85/f1.4 a "near mythical lens". However the "Zeiss" is probably even better.
(If only Minolta had an autofocus version of the 85/f2.0 MD - an absolute gem)
The 100 f2.0 is a gem, but the f2.8 macro may be the sharpest lens Minolta ever made
(except maybe for the 200 f2.
Of the main stream film era zooms the best one can say is they seem to have been "less bad" than many of the Canon equivalents.
But don't take my word for anything...I've been known to state the the lens on my 1957 Autocord is as good as anything on a Rolleiflex. (And I have two)