it's not really a good system, however it is a pretty effective way to limit successful airline on really making that lead and destroy competition.
my current biggest plane is 737, and if there was not that system, any big boy could decide to drown me under piles of smaller aircraft. Currently, they have to be cautious. Bigs can inflict pain to mediums, but are harmless to small, and that's a good thing - there is place for smaller companies. Plus it is fun : it forces you to make choices, & stik to them. Wether they are good or not.
I'm still not sure wether going to London City as a second base in GW3 was a good choice. Because it forces me to use Ejets, who have 1500 orders in backlog... while F928 are as good and much easier to get. But it would be childish to complain, as I also get the advantages of being alone in London City : you can REALLY put high prices over there. Once you get those Ejets... Anyways, that's the way my game is happening, and I have to get the better from it.