I have tried to find out the reason for the strike, but was not able to get any information yet.
Last time they striked (in march or April I think) it was because they wanted better technical equipment and frequencies cleared of interfearences from illegal radio stations.
If they wanted to have a day off they would have done it during the touristic season.
So just leave them alone for once with the cheap cliche of the never-working mediterranean bohemiens. You should go and visit the tower in LGIR on a Monday evening during the high touristic season.
Just let me say that I was also heavily affected by the strike.
Now Heraklion has turned into the calm provincial airport which it is from Nov-March, with about 10-20 flights per day.
So there is essentially no difference. Also the ACC and Athens airport are a lot less busy now.