Officially ex batts ended some time ago to be replaced with the 'enriched cages' , in many people's opinion just a move to appease those that protested over the whole battery cage system. In truth I don't believe they are an improvement.
Most intensively farmed hens (cage,barn and free range) are regarded as spent within the year and that is when they are got rid of. It is only a small number that get rescued for rehoming in relation to the numbers discarded by the system.
You will never be able to compare to getting pol but there is no reason why the majority once recovered from their ordeal shouldn't go on to lay reasonably well, it just takes a little time, as the originator of the thread has already discovered.
I dont know but wouldn't expect that they are fed on inferior feed as surely that would compromise their laying in the factory farm ?
Mine are kept seperate from the rest of the flock on being brought home, given a day to get used to their surroundings then are treated for lice/mites . Worming with flubenvet the 2nd week. Fed mainly on good pellet but healthy treats with protein are offered eg meal worm, oily fish,live white maggots. Quite often it takes their digestive system a while to settle so no extra greens like cabbage/lettuce etc are offered or they tend to get what we call dire rear
which can set recovery back.
Thin egg shell can be improved by adding limestone flour to their feed or even ground baked eggshells help, though very distorted eggs usually indicate a problem unlikely to be easily sorted .
To answer the question was I unlucky this time, I think you may have been, rescue organisation don't go to just the one outlet so maybe this release of hens had come from a less well run farm.