You used that same argument before - and it still doesn't work.
There is no doubt that new aircraft save costs... maintenance and fuel.
But AA's order book is more than 3 times larger than what DL is spending on new and used aircraft as well as mods on its existing fleet. AMR would need to save not only the 3X more in fuel than DL but also the interest on the debt. Remember that the M90s have almost identical fuel burn as a 738 - but probably cost 1/4 of the cost.
What does the size of the order have to do with whether the planes are cash-flow positive and earnings accretive? AA has proposed buying just over 500 single-aisle Boeing and Airbus planes over 11 years to replace MD-80s, 757s and 762s (and probably some of the early 738s with the 737MAX order toward the end).
If 100 new Boeings pay for themselves at DL (according to RA, as I quoted above), then what makes AA's order of five times as many planes NOT cash flow positive and earnings accretive? DL's positive cash flow and earnings accretion predictions take into account the interest on the DL order, so what makes AA's order different? Whether AA had ordered 50 or 500, what matters is the fuel efficiency and maintenance costs of the planes they replace, not the size of the order.
The 100 738s that AA has bought over the past three years have replaced MD-80s and have paid for themselves just like DL's 739s will pay for themselves.
The remainder of your post does not address the primary question. Exactly what does the size of the oder have to do with anything if each plane is cash flow positive and earnings accretive (because it replaces an old, fuel inefficient and maintenance hog plane)? I'm not quoting Tom Horton, I'm quoting Richard Anderson.
You aren't implying that Anderson was lying, are you? He exposed himself to potential securities fraud violations (including prison time) by telling everyone that these 100 739s will pay for themselves. Given that, I take him at his word.
Whether DL can achieve the same goals at lower cost by gathering all the used MD-90s and 717s on the market has nothing to do with the positive economics of the new Boeings (and in AA's case, Airbus) ordered by both AA and DL. Essentially, your position boils down to "an order by DL for 100 new Boeings will be cash flow positive and earnings accretive, but not an order at AA for five times as many planes." Nowhere have you explained why that's the case.