Ninjalooting can never be entirely removed since there are so many different opinions of what it is.
The community can not be held responsible by simply using what the game let them legally do. There will always be players that use what tools are given, and right now the lootsystem gives them option to take whatever they want regardless of actual need.
Name what problems that will come from improving/changing the loot mecanics?
If you simply remove the option to take all items in the entire game with a needroll and let those that can actually benefit from the item you help alot of players and removes alot of problems and frustration. The only ones that could possible be against a system where items are given priority to those that use them are the ninjalooters themselves.
But then again, prove me wrong by stating the new problems that will occur?
Players whine about not earning cash fast enough because they like to sell every boss item in the game?
Players whine about not able to gear up all their companions that they dont use anyway?
Let us know what new problems that might occur by using a common sense lootsystem in a constructive way
So you're proposing creating a problem wherein people cannot collect gear for their companions. Oh sure we could all stop what we're doing in the middle of the run and go about the hassle of trading items around, but it's a hell of a lot simpler for someone to go "you guys mind if I need on that?" "Go for it bro" and be done with it. Once the item is in someone's inventory they're a lot less likely to want to go through the hassle of getting it to the right person. People are lazy, but at least the current system allows for them to be accommodating in their laziness.
Also, how are you going to go about determining if someone can "actually benefit from it"? Oh sure, those boots might increase my Power a bunch, but at the cost of a good chunk of Shield, so is that an item I could benefit from? Do I just have to be able to equip it? If so I can just scoop up all the items that my class can equip and sell them all to the vendor, that's a benefit right? What if I want some adaptive armor for my companion that only comes from a certain boss? Should I just not be able to customize my companion that way?
You, like most people, haven't thought this through. There are consequences to changing the loot mechanics, and none of those consequences is the alteration of basic human behavior.