I had a friend who mained

so I fought this MU quite a bit. Back then it was in Robs favor but now in Smash 4 it's probably only slightly or even now.
Rob can definitively out camp Link if done correctly. Rob also wins CQC considering d-tilt and f-tilt are pretty fast with decent range. Rob can combo Link pretty easily as well due to his weight.
Link however has a lot of tools to keep Rob out and can definitively win the zoning game if played correctly. Link can also juggle Rob considering his landing options are fairly limited.
As for offstage game Rob has the advantage but Link can still pull off some nasty edge guards if the Rob player isn't careful.
In all honestly thanks to Link's recovery being buffed from Brawl I'd say the MU is 50/50 now.