I just converted a fleet of 200 or so planes from a "normal" setup making 75mil a day to what you call a spamline...
my income stayed almost the same.. maybe dropped a tad but its early in the world and there are lots of empty routes. 40 russian planes that were making 300-500k a day on a normal routes are now making 100k a day on 1$ routes.... but my other flights from the hub can stay at the reset price while other airlines lower their fares.
It's a trade off. In long run it will be more profitable I think. I guess you don't really understand something until you just do it and learn. Is it foolproof? No. Now that I kinda get it.... it appears there is room in a large market for several large spamlines to grow and eventually that will lead to an interesting battle, now I get the point of allies and making a plan.
For now... for me... this seams more like a feature than a bug. It adds another level to the game and I don't really see it hurting the average joe... I played for a bit and other than watching income levels grow out of my hopes of ever being in the top... it didn't hurt me as a new player. If there wasn't spamlines... I'm not sure how you would start an airline past the first few months and hope to ever make a single profitable route or find a single empty gate.