I’m by no means an expert on EC261, but I think you will struggle to tie Jager v EasyJet into this. That was a non-binding County Court judgement, but in any case the decision was reached because EasyJet claimed weather on an entirely unrelated flight between different cities which was then out of position. The judge, unsurprisingly, found that EasyJet had not made all reasonable efforts to recover the situation given their size and the amount of aircraft likely to be available at their focus airports. It’s a little used but powerful clause in the legislation.
In this case A3 would have been operating a back-to-back service Athens-Genoa-Athens, so they would be able to claim weather delay (but not mechanical) if the incoming plane was delayed by the same weather issues that affected your flight.