Last night I decided to rebuild my airline, and started in Santiago, Chile. I opened numerous domestic routes within Chile and a few international ones, as well as opening a base in Dallas, Texas then deciding that airport was fairly saturated, closing the base and opening one at Fort Smith, Arkansas. I then opened multiple domestic routes from Fort Smith and upgraded the base size a couple of times attempting to get more slots, but none were awarded. After almost a day, my service level has increased to ~3 and all my routes from Fort Smith are at 100%, but I've still only got 10 slots. I have, however, got more slots since starting in Santiago.
https://i.imgur.com/FtjmfaG.png