+1 with Talentz. What is true in some circumstances, is not in others.
My fleet choices in Vietnam(55% relative staff cost) are not the same than in the USA(192% relative staff costs). They are not the same in HAM(lots of medium European destinations) than in ARL(huge domestic market concentrated on a few short lines). They depend on opposition or kind of game(I went full DC9 last regional challenge, in the 2015s, and I was first in all rankings before real life called me to heal my son - in a normal game, it could have been suicide). I'm flying nearly only 7-7 schedules in GW3, but none yet in GW2(it has to change, but for starting reasons, I could not dream about beginning like that). I flew pax leased IL96s from Algiers, and actually did profit for a few years with them. I filled Europe with Fairchild metros and had 609 destinations, pre-cargo. I owned more than 50 IL12s last GW2 in WAW, and they actually gave me an edge against my opponent there. I have not ideologic problem flying 12345_7, even LH if the situation justifies it.
I never BK'd, I was 14th in scoring in ALG, 8th in score in WAW. I think I can say I know how to play. Absolute rules are far from absolute. 12345_7 transatlantic flights have their use, for example, which I learned mentoring one of the best players of the game. I'll keep it for me, that's very advanced tactics. It's a bad idea most of the time, but there are cases when it's kickass. Despite losing 10% of plane use. Cost is not everything. One has to look at the overall picture.
748 is overall a dangerous plane, like the metro, like the IL96, like the A148(I flew 720 of them, once, before the achievement), like most soviet steel(bar the SSJ). It is still playable, and can be, in some circumstances, be the best tool for the need of the moment.
But that's often a question of skill. I'm pretty sure Schro, Frimp or Elladan can kick most of our backs using only soviet steel scheduled 12345_7. Conversely, a good but not excellent player will be exterminated by the best players, even if he follows all the guidelines. I can see them, the guys who stick to "best" fleet groups, have excellent scheduling, but fail in using it the bast way as the game unfolds. The best players, IMHO, are able to adapt their plans to changes, while the good ones simply follow their plan. And that's a biggest difference than using 12345_7 against 7_7, or using the best airframes against surprising ones.
What is important is to understand why, in most circumstances, 748 is dangerous. Which tells you when it might be a better idea.