Legacy Items and why they weaken the game

When something is OP to the point of limiting build viability why would you leave said failure in the game? No other games do this because it doesn't make sense and adds nothing to the game. It is impossible to have a real discussion about this because the people who own them will be the loudest most vocal voices with whatever happens. Old Koam's Heart among other items break the relative game balance and make the standard leagues a cesspool.

The argument for them is "I was here first" and that is really it. If they are retroactively nerfed that would balance build strengths and make standard leagues better for almost everyone. GGG could give everyone who owns one an exalted along with their proper item and everyone would move on happily. Not saying for every item change but this could be one of many options GGG could use to deal with the OP legacy items.

I would actually like to hear one sound argument on why a broken item isn't bad for the vast majority of the player population and the how Legacy gear is good for the health of the game.
The theory right now is we'll make permanent changes but not everyone has to embrace them - that just doesn't make any sense.