Yeah, with regards to the 753 though, they could be onto a winner with it if they tried, just put it on all the trunk routes, 2 A321, 1 753 instead of A320 and swap the routes around a bit.
Edit: Regardng 737NG vs 757, its all relative, when you say of all models, there were only 2, ans the second one came along quite late, the 737 had 4 (Technically 6) which went from low end 120 seats to high end 200 seats, the 757 was all high end 200+ seats for the most part. Then there's the fact that many NG orders will have been to replace classics and that the 757 was more expensive. But still I see what you mean, 3500 more is a lot more planes. I think the 757 could have made 2000 if they'd kept it on until now, there's a lot of them needing replacing (effectively)