I guess we have to determine if the entire argument is moot -- do we even know that these airlines took huge "mega-loans" to build their empires?
Even before the new system that was implemented this round which is far more generous with the money than the last in my experience, there were players that could attain huge fleets in very short order. They're not taking out huge loans, they're "gaming the game". They know precisely what one needs to do to earn huge rates of return, expand the fastest, and earn the largest sums of money as fast as possible. You can see it now when you look at the Stats, but it's even more evident in the opening months of the game; these players are ordering numerous brand new planes right from the very first day and only expand exponentially from there. A small handful of players, I presume having played countless beta games is a huge help, just know precisely what they need to do to grow incredibly fast. I'm sure loans play a part, but it's definitely not the driving factor of their growth.
I'm sure my competitors in DFW in Jet Age #1 are thinking the same of me, even while I look at others that are leagues beyond me. My competitors all started at the same time as me, but are struggling with 1/4th to 1/10th the market-share that I have, and only able to order small handfuls of narrow-bodies at a time with total order queues that can be counted on one-hand. My airline on the other hand, has got Sixty wide-bodies on order, and has had as many as over 100 total planes on order at once.
And, no, loans have hardly played a role at all. I've really only taken loans if it means taking a small one to get an even 10 planes on order rather than the 9 I can afford with cash on-hand, and I immediately pay it back.