Alonso surely is one demanding guy ..as a f1 driver should be .So yes he is a huge factor in turning around the fate of a team.
He started this already last year in a very positive way never giving up and spurring the team on to go that extra mile...and it almost paid off.this year again he´s not willing to admit defeat when everyone is already seeing Vettel as the champ.
Costa had to take responsibility as Ferrari is expecting clearly better performance over the year..and it seems Ferrari does lose the plot every year sometime.