I am running a custom campaign as DM with two players, P1 and P2. P1 plays as a Druid while P2 plays as a Warlock/Rogue whose game style is based on being stealthy. I let P1 find a Staff of the woodlands which, among the varius properties, lets the character cast Pass without trace (+10 to Stealth checks) without using slots or charges.
P2 asked me to let him find a similar item, since he often needs Stealth checks. At the beginning I pleased him with an item with the same effect, but then I realized that it needed some limitations, since P2 already has +11 to Stealth and therefore (almost?) every check would result in a success with the new item.
I stated that I wanted to introduce some limitations for the next game session, but P2 complained saying that this is unfair, since P1 has the same item (with additional properties). Also, I could not change the properties of an item that I had already introduced. I replied that P1 doesn't have +11 Stealth (and he never will) and his game style doesn't include a lot of Stealth checks, so the problem does not exist for him.
Now, after this long introduction the question is: is my reasoning correct? I tried to consider the characters skills and I realized that the game was going to be unbalanced. I am a novice DM so please tell me if I should behave differently.