Something in the way rewards for a battle are calculated is skewed, & the game seems to be deliberately withholding the items you are trying to get! I've spent an entire energy alotment trying to get 4 of an item I need 20 of, refilled for 50 gems, and used all that before I got them!
Also, the more gear items you collect in a day, the fewer you get, so spending gems to refill energy becomes pointless, but there's no other way to get the items.
This applies to shards too, the more stars a character has, the more battles you have to SIM/win to get the same number of shards
