For me Aguero is a 30 goal a season man, with those round him adding 8-10 each. But Pep would prefer all forwards getting 20 a season each.
I think summer 18 is the natural progression for him to leave.
The bigger problem is that Sergio was a 25 league goals a season man in a team scoring 80 goals a season.
Now he's in a team that could score 120 and he's still looking like a 25 goal striker.
Pep's shown at Barca & Bayern he has no problem with scoring dominated by 1 player, but in a team that creates so many chances, that 1 player needs to be getting 40-50 in all comps.