For the strike situation they are considered extraordinary circumstances and have a specific carveout that releases the company from the responsibility.
For the regular cancelled flights, I have a long trail of evidence where with Lufthansa call center we got to the point of agreeing on the refund and providing the banking details, and then they went silent. Had to go to one of the companies helpfully doing the same for just 30% commission.
Again, the strongest evidence that it's difficult to recover money from Lufthansa (airlines in general) is that there's a whole cottage industry of companies who exclusively deal with this. No customer would agree to pay 30+% recovery fee if the airlines were forthcoming with fulfilling their legal obligations.