The main issue with this team is that they can't help each other's recoveries. Both of them do pretty porly vs MK as well (but not terrible). Luigi can help with the Falco/Diddy's of teams and Link can help Luigi approach as said with projectiles. In general they play off of each others' weaknesses.
Link can force an approach, Luigi kills like a madman.
+ Both characters are terrific at DI
+ Link can help Luigi approach/ "combo"
+ Luigi helps with the Falco/Diddy/D3 matchups, a LOT.
+ Both characters do well vs MK when they can force MK to approach, teams force MK to approach in general.
+- It isn't a common team, people won't have experience vs it
- Recovery.
- Is it the best Link teammate, probably not
- It is one low tier, one mid-high tier, no tierwhoring for money,
Out of 10, I give it a 7.5 Lean more towards a 7 if the opponents have actually faced a good link team, more towards and 8 if they have not.