I think you are being more than just a tad unfair there.
That the A321 has evolved into a magnificent short haul frame, there is no doubt, acknowledged even by Randy Tinseth at Boeing. Indeed, he views his company's rival to the A321 to be the B737-900ER, not the -800.
I rather feel the 738 will be left somewhat lacking on some of the routes you mention. MAN-BJL, for example, can typically have a sector length of over 2910nm. The Boeing "brochure range" for a 2 class configured B737-800, with winglets, is 3115nm. Go for an all economy config., and that figure goes south, quickly.
As Tinseth himself claims, the B737-900ER is the better candidate, by a small margin range-wise, but other than the defunct XL, the charter carriers have hardly been flocking to buy it, have they.
It wouldn't surprise me if Monarch decide afterall to go with the A320/321 NEO in the future, offering yet more range with improved economics; then we can be done with all these "The A321's no B757 replacement" comments; it was never intended to be, but they are slowly getting closer to achieving it, whether that was Airbus' objective or not.