Originally Posted by
hkgg
The pilot said, in one sentence within one announcement, after boarding has been completed, that because the flight started boarding late, we have missed our take off slot (even though there was only one other flight departing within the next hour), and, that there appears to be a thunderstorm en route and so, we would be delayed by roughly 30 minutes.
This is the paragraph that undoes everything. You have both an ATC delay and weather en-route. That's two reasons for citing extraordinary circumstances.
The flight may well have been smooth - that's probably because the plane was routed round, over or under the storm. That, in itself, causes more congested airspace because there are certain flight paths or altitudes that can't then be utilised, so ATC will slow the flow rates through the affected areas.
That, in turn, impacts on when you can take off - so the weather at origin and the number of flights going out are not relevant. No pilot will take off, reach the handover point to the next ATC, only to be refused access to the airspace and have to fly around in circles for the next 20 minutes!
Based on everything we see here, there is no delay compensation claim and A3 has already discharged its responsibilities on Duty of Care.