The commonality trout slapping is not aimed at simulating reality but rather a game play balancing function. It forces strategy decisions to be made and followed through on in order to survive..... it also contains the growth rate of my small regional airlines as a result. It's annoying as a player, but it also wouldn't be fun to have a handful of huge airlibes in each world grow like weeds and make it no fun for the average player.
This, from a player that is good enough to eat all the USA market if given enough freedom(i.e. enough fleet groups and no limits for planes outside HQ). Those two rules, punitive 4th fleet group costs, and hard-coded limit on planes outside HQ, are designed for game balance, not for realism(they are all but realistic). They are really useful. They force you into making strategic choices. They force you into interesting choices. You cannot cover everything. You cannot go from the 777 to the metro, with 737, Ejets, and ERJs in the middle. You must either go small, which gives you more survivability in frequency wars, but less potential, or go big, with the reverse situation : lot of potential, but more vulnerability in frequency wars.
@KestrelAIH : if you get what you want, Schro is going to eat you for breakfast. With a MD90-55 sauce. Me too, by the way, would be on his plate. Realism is good, but only up to a point, in a game.