Perhaps this is only in non-open worlds, but unless I'm flying from ATL, there will always be at least 5 routes with more than 200 demand and none to very little competition. YYZ and HND are among the biggest airports in their countries, so you can expect to meet competition. Flying between secondary european airports I can connect a least 50 airports using daily+ E-Jets without ever meeting competition.
ATR are quite efficient and cheap turboprops in the 50 - 78 passenger range. You'll find them where it says 'ATR'. Shorter flights make more money than longer ones.
I'm going to be trying this approach whenever I get onto a new server next. Aim is to see how much I can make with smaller planes and smaller locations.