3% is a lot...
3% may well get you a seat on a board, you do not need to have 51% of a company to get them to do what you want, 15% or even 10% may well be enough to control what Sharp do.
I think it is a great idea from Samsung, Apple can't walk away that easily, there are only so many companies that make the sort of quality screen Apple want and you don't set up a new fab plant overnight. The more Samsung owns of the supply chain, the more they can dictate what happens. An army marches on its stomach, Apple lives on getting units unto the shops at the right time, if they are no longer at the front of the queue, Apple will suffer financially.
Sometimes Apple is really, really smart, like when they brought up a large chunk of flash memory five years in advance and sometimes they're really, really dumb, like when they sued World+Dog over any IP infringement they could dream up.
I see Apple wining battle after battle but losing the war.