Rakitic early on also had to deal with Lucho's tactics when he was just finding his feet at the club. We didn't have a consistent XI (How many months did we go without using the same XI twice?). Rakitic had to spend most of the game covering for a Dani Alves who was almost completely ignoring his defensive duties in favor of linking up with a Messi who at the time was still playing centrally. He clearly fit into the team and was able to keep up with the other players but what he was instructed to do limited his abilities. It's not just a case of him adapting to the team as time went on, his rise to form coincided with the entire team suddenly meshing together after *that* game at the Anoeta, imo. I think a lot of the negativity surrounding Rakitic was also largely steeped in the overall negativity surrounding Lucho after we lost to Real Madrid so humiliatingly (That's also the original "Mathieu sucks at LB" example, looking back).
I don't see any real connection between that and a 40m, 29 year old who isn't performing any better than the midfielders we already have. It's already clear he won't be a starter, that much has been certain even to those of us who were initially infatuated with him, and to those who still are for some reason. With the likes of Roberto, Rafinha, Denis, Halilovic, etc. coming up, with Samper, #TeamAlena, Kaptoum, etc biting at the heels of the first team in the years that would be Arda's 32+ y/o veteran years, it's hard to see him sticking around for more than a couple of seasons, especially performing on the level of a squad rotation player.