Dudes, I feel you. There's this one Link player I just haven't been able to beat recently, but let me tell you what I personally try to do in the Link MU.
Okay, so a big thing I noticed in 3.0 was that our Fireball actually cancels/destroys all of Link's projectiles. It explodes the bomb, cancels out the arrows and it used to cancel the boomerang. The only difference with the new update is that the boomerang is just sent back to Link instead of being destroyed. I don't really use this on the bombs because a lot of the time the bomb may fly over your Fireball and you both just end up taking damage. With the arrows and boomerangs though, the Fireball should eliminate the challenge of the walls of projectiles. If you're not too confident in your fireball game, remember that you have generally better movement than Link, so use this to your advantage as another option to avoid the projectiles. Link, as mentioned does have disjointed hitboxes along with a pretty good range on all of his attacks, so the next challenge would be to find a way in past his attacks. SHs along with SHFFLs can make for a pretty mean wall of attacks too. So, Ftilt will be a good friend to you here. Slide around trying to bait out some of these aerials and strike with a nicely placed Ftilt and you should be good for this. Also, Luigi's aerials all come out pretty fast. So, some nicely placed aerials should make it past some of Link's slower starting ground attacks and even aerials. Finally, I would say making it back to the ledge or even making it back up to the stage from the ledge would be the hardest part of this MU. Since you're now in the air, most of your ways to deal with all the projectiles have been completely done away with. You're now down to your fireball (which I would use only for the arrows if you're horizontally distant from the ledge) and your aerials which would cancel Link's projectiles without harming or pushing Luigi away from the ledge (with the exception of the bomb). If you make it past all the projectiles though, your next biggest challenge will be Link's Nair. Link's Nair hitbox has to parts, one on the extended leg and one on the bent leg. The Link player I'm having trouble with turns his back to the ledge and uses the back leg hitbox, which is significantly lower and big enough to cover the ledge if done low enough to the ground. This will stop you from grabbing ledge, but if you Up-B high enough, you should be able to either try and sweetspot the ledge with Side-B or hit Link with a Side-B. The safer option would be to try and clear Link from he ledge using a fireball and then immediately going for the ledge.
Hope this helps, guys!
