I would agree with OP that air traffic will be very slow to recover (5+ years). Some more issues that weren't mentioned:
1. With the potential for lasting new procedures and screenings at airports (e.g. temp checks, travel history, social history), at both the departure and arrival airport, air travel will become more of a pain than ever before, reducing demand.
2. Many businesses are now seeing that virtual meetings can work for them, and they won't have to keep flying employees all over.
3. Ongoing uncertainty about restrictions and quarantines. I've been wanting to book a family trip to Europe in the fall, but I'm not sure if it will even be possible with the likelihood of another resurgence and more travel restrictions. It's not worth risking booking the flights and hotels at this point.
4. Even if demand magically comes back in a year or two, the supply will not be there. Airlines are now permanently retiring airplane fleets, planning to lay off employees, halting training, and cancelling future airplane purchases. This trickles all the way through the manufacturers too. It will take years for the supply chain to recover and to train new employees.