Yeah, Alves is pretty much impossible to replace. The only other player who could do it is Lahm.
You need a new, quality DM. Ever since Toure left this has been a weakness Barca can't ignore any longer. Tiki Taka won't work against big teams anymore so busquets has to go.
That transfer ban fukked you guys over, imagine Arturo Vidal and Hummels in your backline. Everyone wants to play for Barca. Unfortunately There aren't that many good defensive players currently.
I know....Alaba was ready to make the move but Barca didn't want to have him play CDM over Busquets or even convert to a 4-2-3-1 because Messi and Neymar are the only true wingers and Messi playing centrally would leave a weakness on the right side. Umtti will be world class, and Barca failed to secure Bellerin from Arsenal or Aurier from PSG.
I don't think Busquets is so much the problem as he needs another truly amazing distributor next to him. Iniesta, for a glorious as he is is aging, and Rakitic isn't having the stellar season like he did in 14-15. And for DAMN sure Rafinha isn't a good replacement for either. Sergi Roberto's growth was stunted by having to convert to RB when he should have been on Loan, somewhere, starting as a CM.
In years previous Barca had the coaching to go with the talent...I don't think Lucho is the man right now. Barca CAN play swashbuckling football when they want to, it's just that the security blanket of Alves/Alba/Mache/Pique is not there.
