I'm not sure the advantage is THAT extreme.
In Jet Age, for example, I started 5.5 years late... and am currently 10th out of 150+ airlines in terms of CV.
I suppose that the advantage will be greater than in old versions of the game though, as it's possible to join an old game at an airport where a company didn't work out or retired and thus has plenty of free demand... in 1.2, that would just mean someone will start a new hub there.
Prove me wrong. I would have you BK and restart, then tell me your Feb '98 start date wasn't "game winning", depending of course on your own personal criteria. If you open when the game world does you can max profits for the first 6 months and dominate the viable production lines afterwards. Thats the advantage, period. Like I said, I'm not complaining. I don't personally want a game that starts at 0; I greatly prefer to have to carve out a niche and survive. I'm saying for most of the players that ARE complaining, it's a case where in order to be hugely successful (again, personal criteria apply) with a large route network and modern fleet, you pretty much had to start when ATB did. Otherwise you're just doing the best you can to survive.
This, and the other, 1.2 game worlds are barely 15% complete though. It might be quite easy to do as you described in the 50-75% stage; nobody really knows for sure. However, the trend so far suggests that this is not the case. Have you taken the time to imagine if you'd opened your airline with fuel at ~500, viable new productions lines dominated until ~2003, a still-very-much-competitive used aircraft market, and the threat of 9/11 looming just a few months away? While I may not be in a terrible position myself, it's by no means a stretch to sympathize with the players that ARE in this exact situation.