In fairness, Ven did say 'slow' in addition to poorly conformed but you're right Kri, it's illogical to say that some sires who performed badly but made good sires should be lauded, while you can point to many mares who either had poor race records or maybe didn't even race who also were good producers. Where do you think the slow, poorly conformed mares usually come from, anyway ? Far more likely to be from lower quality stallions than from those good-looking horses with decent pedigrees and race records!
You should remember the stockmen's adage that the sire is half your herd - and that applies to horses in the same way it does for sheep, cattle, pigs etc. One male will, on average, produce many more offspring than the average female, so it makes sense to try and preserve only the best males as potential producers. Of course there are examples of 'poor' stallions producing the goods but again, the horses you are referring to, Ven would have had very limited books. It might seem logical to assume that they were breeding above their level but, if they were being used today with books several times larger, would they then have sunk out of sight with more uselss racehorses appearing for them ? Who knows, but you can't rule it out. If they hadn't been allowed to breed, something else would have taken their place and who's to also say the progeny of those mares wouldn't have been even better ?
We'll never know because equine genetics is still pretty much of a lottery and that's what makes the whole process so interesting - ecstatically exciting one minute and then utterly depressing for the next ten years. As I've said before, racing attracts gamblers in all sorts of guises - I may not bet more than half a dozen times a year on horses in races but my gambles are just as big every time I send a mare to a stallion.