The issue isnt that more so, its for me the server load with a large airline, and how you still haven't realized there is a limit on growth in AE that isn't imposed by rules but rather natural and the fact that I could later on , with 757s, create an airline running big routes 2-3x daily, full price and make a tidy profit
Step by step and, if anyone knows a more precise response please feel free to add their insights:
1) Regarding server load - common sense, it comes rather from the amount of routes to recalculate rather than from a specific airline. In a world (e.g. R1) designed to run up to 300 airlines, the size of 1 reaaally huge airline and its routes will still be no more than the equivalent of 2 or 3 airlines from the top 10, or in other words, peanuts regarding any marginal increase in server load.
2) The limit on growth in AE is the starting amout of traffic generated by each airport multiplied (surely yearly) by a growth coefficient that I presume (again, common sense) is probably taking as a reference a normal GDP growth or something similar (between 2% and 5% increase yearly in global passenger traffic in all airports). Therefore, the limit of that "natural growth" is predictable and feasible to achieve by putting as many seats on the market as deman available (or something close to it if willing to achieve monopoly) and at a price tag that would make inneficient to operate anything on that route that is sub-obtimized in terms of seats and airplanes.
3) Finally, if at some point you happily join a saturated market with 757s and start flying 2-3x daily, lets assume, all the available big routes on top of the offer provided by the existing competition, yes, you still will be making profit and, therefore, that's the whole point about whining - anyone who have passed maths at the elementary school could run a sustainable airline in any scenario given how friendly AE is designed and regardless the amount of huge or megahuge airlines operating in your world
I hope this helps to shed some light and provide a better perspective on the game dynamics to realize that a simple calculator at hand can be much more useful than a tonn of whinig rhetoric suggesting that the world might be sometimes unfair because of poorly managed airlines and... egos
PS: As long as the cash sitting on the airline's balance sheet does not generate any kind of interest for the airline, business wise it's also common sense to keep investing in planes and making them fly because as long as they are in green your return on capital will be higher than just having your money on the airline's account doing nothing