Just one big plastic cup each once a day I think I'm overfeeding
Unless it is scratch or an inappropriate treat, you can't overfeed chicken feed.
There may be issues with waste, etc. but they won't eat more than they need.
You could actually be under feeding. Is the once a day feeding in the morning when the chickens are hungriest? Is there still feed in the feeders at dusk? If the latter is negative, they don't have enough feed.
What kind of feeder are you using?
Also, you can't compare the quantity you are feeding with what other people are feeding unless you have the same breeds.
A Serama weighs less than 500 grams. A Jersey Giant or Brahma on the other hand could be between 8 and 15 pounds. Those breeds will eat drastically disparate amounts of feed.
Unless one is raising Cornish Rocks for meat, during certain growth periods some may limit feed. Otherwise, feed needs to be available all waking hours.
Chickens are not dogs. When chickens' crops are empty, they are hungry and will eat something. Do you want that to be a nutritionally complete food or bedding/feces?
One big plastic cup doesn't tell us how many grams/ounces of feed you are feeding nor how many birds are being fed and what breeds - LF or bantams.
It is an apples to apples thing.