The 767-200ER does not burn much more fuel (about the same amount comparing the max range 752 compared to the min range 762) and does not need any more staff and only has 10 more minutes of turn time.
It seats a few more people and thus enables for growth over time, to which every route is subject.
I don't know about the difference in maintenance cost, but it can't be that bad.
So where does anyone need a 757? Also, you save an additional fleet type if you also employ the 763 and 764 for denser long haul routes. So any potential savings on maintenance that I might not have considered become irrelevant due to the savings of having one less fleet type.
Actually, turn time is 20 minutes higher for 1% (115 v 135).
The fuel is close if you are ordering new and get get the most fuel efficient, but could be 10% more or worse when you get them used.
Staffing numbers are the same (2 pilot, 5 cabin crew) but the 767 needs very large pilots, who earn about 30% more. They also need more actual pilots to cover the 2 per plane. My fleet has 48 very large planes, so 96 very large pilots, and I employ 860 of them (9 per seat). I have 45 large planes, 90 pilots, and employ 450 pilots (only 5 per seat). So while both planes need 2 pilots, the actual cost of those pilots is more than double for the 767.
Large vs very large also means a difference in landing fees, etc.
You also missed one other fairly big point. The 762 costs more than 400k/month extra in leasing fees over the 753.
So if you don't need the range of the 762, the 752 & especially 753 are definitely better.