under 'normal' circumstances i would agree.
However, we have another year of European football and we have 12 players at this year's World Cup.
By Christmas there will be injuries and fatigue in the squad, just as there were the season last gone.
If Pino doesn't play the left side 10 (or needs to be subbed after 70 min) who can fill that position? Currently it's Devenny, who is very limited. The other option is Guessand who will cost over £25m. That's a lot for a squad player. Johnson has proved on multiple occasions he cannot play that role.
Ayew on a 12 month contract is a decent short term solution IMHO.