I agree, I have 3 of my 4 bases at 50K airports. They are very profitable, yes, they won't make 100K on every route, they're not supposed to, but since they are not in large interest to most players, and most players can't even locate these places on a map if their lives depended on it, the competition stays low.
I'd try avoiding making bases at larger airports (200K-300K) until you grow more powerful and can afford to fight hard in such markets. They are huge with many players and competition is very tense. I notice usually 4-20 seperate flights on routes that I fly to the largest airports in Europe (LHR, BRU, AMS, and CDG).