As you said yourself said this is a force majeure situation and it would be wrong to punish an airline for something that wasn’t really their fault.

Saying “but X airline chose this software” isn’t IMHO going to work.

For example if airlines choose to cancel flights from A-B if ATC flow controls are implemented doesn’t have to pay compensation even if another airline does manage to fly the same route. Yes the airline made a choice of which to cancel but equally it may not really had much of a choice at all. And at many airports the major carriers there are going to be hit much harder. Take AMS for example restrictions are always going to hit KLM harder than a once a day flight airline. Is it fair? Not sure but it recognises that the likes of KLM have much more flexibility to rebook onto their other flights to the same destination then the one or two flights a day airline.

And the courts and regulators have recognised it as well and basically said in those situations compensation isn’t due.

But even airlines whose own systems don’t use this particular IT product were affected because some of the airports they use did and were either basically closed or severely restricted operations. And it’s also the case where the vast majority of their systems were unaffected but something like crew rostering was amd that is definitely a flight safety issue.

The exceptions list in the regulation isn’t a definitive list of exclusions though it’s more of a list of examples. The courts have refined the list as well. A strike within an airline by say its pilots or ground staff isn’t an exempt cause but a strike at an airport or ATC is.

Passengers were not totally unprotected. Duty of care provisions kicked in so airlines are on the hook for costs of refreshments and hotels if one was required.