Allan signed for Napoli in the summer of 2015, the same window we lost Vidal. We signed Khedira to replace him instead.
At the time Allan played for Udinese and was still unproven at the highest level, but Napoli took the risk and it paid off.
There is no real excuse for our midfield being as weak as it is. There have been plenty of talented midfielders playing in fodder Serie A teams (Allan, Torreira) which we easily could have signed but decided not to, because we’d rather give Khedira a contract extension and a raise.