That's what you are assuming. The polish passengers arrived by car (the drive to Berlin is much shorter than the drive to Warsaw), rail and by air (AB feeding themselves out of several polish cities, including Warsaw).
Yes some tickets might have been a bit cheeper than on LOT*, but there have been parallel flights by UA to EWR and (before that) by DL to JFK. A recent flight from TXL to EWR has shown me there's still a good share of Poles using this opportunity.
On top, AB was feeding AA's focus in JFK and hubs in MIA and ORD, much like UA was feeding their own hub at EWR.
Hainan to Beijing wasn't too shabby either - just like Qatar and Scoot.
There have been succesful intercontinental routes for years and they're still persisting. Whether those were daily, daily-double or just once a week is of lesser importance. It's a lower-volume market that FRA or MUC, yes. It still works out, though. In fact, AA was quite happy being served by AB. That lasted until AB started selling tickets into DFW without prior consulting AA.
Berlin was and still is severely limited by a couple of external and self-made problems. One of them is the lack of industrial and economical strength, which is very slowly recovering**.
The next is the lack of available hub-connections possible, which is self-imposed by the BER-clusterduck. Fun-fact: TXL was supposed to have a subway-station below the connection between it's first and second hexagon. The second hexagon (and the subway-tunnel) never materialised. There was going to be BER, right? Well, Terminal C had to take up the slack and now serves EZY.
Another one is the already mentioned lack of parking-space on an airport that had never been designed to facilitate long-haul connections during peak times. Shuffling any amount of connecting pax through this ancient airport for intercontinental transits has been a major pain in the butt, as well as a monetary isue for AB. The amount of lost baggage is mind-boggling. I once had the chance of claiming a lost bag (fortunately I had an airport-badge) and visiting the lost-baggage area. An absolute horror-picture: Thousands (!) of lost bags waiting to be sent forward to their owners. Some of them half a world away...
Last but certainly not least is the comedic ground-handling.
Want a GPU? Wait for half an hour. Want a working GPU? Well, beats me...
* AB's yield management was one of their demises.
** With the city-state's government, I wouldn't placy any bets on it, though...