Loot pool dilution means players who paid for the premium item find it much harder to level up any of their items because the chances of equipment and material drops are lower
It’s understandable that the devs don’t want it to be too easy to upgrade (they would rather that players purchase Epic/Legendary Gun and Tinkering kits, priced at ~50 USD/~100 USD respectively), but the current method actually penalises players who have paid for premium equipment.
This was originally posted on Reddit and the idea I like most (from FieldMouse007) would be give a lock-out option for every piece of Premium equipment. Then the paying customers have the same chances of getting what they need as the F2P players and are more likely to continue to buy.