Two major changes made in the last 2-3 months are:
Frequency now has a much lower effect than previous games
Smaller planes do have a disadvantage if you are flying longer routes with competition
In other words your competitor may have more 'appropriate for the routes' planes, and the recent changes were made to give this aspect of gameplay a more 'even balance' than before where frequency was king.
Perhaps this is where your problem is?
There is a entire thread devoted to the beta testing of the changes as the changes were significant to gameplay (sorry but I can't find it, but someone else may be able to provide the link)
Or you can ask some of the more experienced players e.g. Sanabas, SAC, Swiftus27....aha I just realised why I can't win at this game...my username doesn't start with an 'S' :-)