For sure Gearbox will do something about the invincible combo of using a low level Stop-Gap with anything that can refill its shield very fast.
To prevent future “farm low level items” breaking the game and so that Gearbox doesn’t have to balance items around it, here’s a simple fix.
Once a character reaches level 50, any items that aren’t equal or greater than 45 become level 45 while in possession of the level 50. The items would still be their low level but give level 45 stats/effects.
In other words, you have a level 5 item in the bank you saved for an alt. You hit level 50 and decide to try it out. The item becomes level 45 once you take it out of the bank. If you later decide to put it back, it goes back to its original level. If you trade it to someone else, it will be its original level.
If you are somehow using level 44 or lower items when you hit 50 they all become level 45 as long as they are on you or in your bag. If you trade/bank them they revert to their original lower level.