There are only five groups of wormers, and three of those groups are heavily compromised. In some areas a significant proportion of worms are resistant to treatment, and there are no new chemical treatments in sight. Without effective antithelmic drugs everything changes.
There are other approaches to worm management but they don't allow for intensive production. Sheep and Cows share the same worms but Horses have a different set. This year's eggs turn into next year's worms, but if the right host animal isn't there then the cycle is broken. So swapping sheep for horses each year, or growing hay instead of grazing will achieve a good result, but at a cost.
This is why it's important to get worming right, and that means knowing what it is your trying to kill and using the right tools in the right way.