I can agree that it isn't optimal flying out on QR, however not very busy in the evenings, I was on the 21:50 out of ARN, arrived from LHR 4h before, then the passport check was manned. The lounge nothing to write home about though.

Flying out on BA from ARN is very good though, if you can fast track through security time to lounge is similar to the First Wing at Heathrow and departure gate a 50 meter walk from the lounge, so will not agree it's terrible in general.