Recovering full-blown addict here. All I can say is "dream on". People have been suggesting this since I started playing here 11 years ago. I think I was even one of them. It's a miracle this game's still even functioning.
The site's been boken in a number of places for some time now. My son who's studying IT at university had a look "under the hood" & identified a number of coding issues within seconds. All game worlds function but some better than others it seems. But yeah, maps seem to be too hard for it now.
What was your daily pax level? In my opinion, while you can start to feel the effects with just a few hundred thousand, you really need > 1m daily pax. Also only 4 hubs aint much. Try 40. Hub EVERY airport you fly to/from. I general only focus on green pax at standard capacities & prices till I get to this sort of level. Then I go nuts. It takes a lot of planes & a lot of time. Good luck.