The argument for it sticking around has to do more with theory than anything. That Tin Link creates an environment where attachments are assumed to be almost useless would create a new theoretical consideration for designers. This may induce them to create new attachments that are unbalanced in an environment without Tin Link.
There's no real evidence whether or not restricting/banning Tin Link will have a positive effect on the game. It just currently has a very visible and incredibly powerful effect on one card type. Ironically, that card type has been so underpowered for so long that you could effectively scrap attachments and Tin Link altogether and I doubt anyone would notice with the exception of Targ for a few recursive burn cards.
Is there anything to truly be gained by banning Tin Link at this point? I would say only if FFG actually wants attachments in the game. One consideration for why there has been no change to it could be that FFG doesn't like attachments, but that's just me hypothesizing. Banning/restricting Tin Link at this point in time could dramatically destabilize the environment and create imbalance in the houses.
Being the governing body of a game can suck, haha.
Without Tin Link, attachments are still going to be carefully analyzed as being good for a deck because they are still fragile. When a card leaves play, so do all the attachments attached to that card, so attachment hate can be lumped into the category of hate for the card type they are attached to as well. There still exists other attachment handling options out there as well, but Tin Link provides the easiest and most efficient way to deal with them. Without Tin Link, at least attachment hate will need to take the place of a card slot in your deck that needs to be drawn just like any other card type hate there is.
I can't really think of attachments that they may create that would be unbalanced if Tin Link were at least restricted. If really strong attachments are used, then the player base should evolve and add some of the existing attachment hate that actually takes some card/plot slot sacrifice, cost, or effort to get going. Evolution is the concept of an LCG. The player base would find certain cards to be a common use and thus be prepared to face them in their deck building. With Tin Link, it generally makes any deck with more than 1 or 2 attachment types of cost 2 gold or more(1 gold if the attachment has a crappy card effect) a terribly inefficient deck that has wasted slots on cards that you can't use in a high percentage of games.
I think if the chain attachments had more effort in their trigger, they'd be more acceptable. For example, the following chains trigger off the character kneeling(and a summary of their ability) -
Bronze Link - Return top attachment to hand.
Pale Steel Link - Put into play attachment or character 1 cost or less.
Tin Link - Discard 1 non-Chain attachment from play.
Steel Link - Choose and stand 1 location.
Iron Link - Choose 1 character. Until the end of the phase, that character gets +2 STR and gains a icon.
Black Iron Link - Choose 1 character. Gains or loses INT icons.
Some of these(emphasis on SOME because not all of these are retarded like Tin Link and some should be generally easy to trigger during the challenges phase otherwise they'd be useless) could have their trigger changed to "When attached character stands." and it would then require some deck building effort or for some decks, the standing phase, to trigger the affect. Instead of paying the cost of other effects, initiating challenges, and basically triggering off of Lannister kneel effects, you can then use the chains effect if you can find a way to stand the character. If you can find a way to stand the attached Maester, then go for it. However, at least it will take that next step to trigger the chain. If this happened with the Tin Link and maybe the Bronze Link, then maybe it could be more viable… the problem still remains that the triggers would still likely be once per round, but at least you can get through a challenges phase without feeling like any attachment you have in play will simply be discarded before it can be used.
I am more a wishful thinker than anything in this game. I bet if I designed the game, it would be awful.