Forgive me, I'm not particularly well up on how successful ZB is at LGW but I think that the problem with routes like GRX and LIS is that their aircraft are too big. Filling an A320 or 321 on a regular basis on non-bucket & spade routes is going to be more difficult than filling a 737 or 319. If ZB really want to make a go of more cities/business destinations than perhaps they should look at adding some smaller aircraft to their fleet. A319's would be the obvious choice with the majority of their scheduled flights already operated by Airbuses. Even if the likes of LIS have been doing ok, they know they can utilise 174 or 214 seater aircraft better on other routes and that's what they've done.
I admit, I'm a little surprised to see MAN-XRY dropped. It has done very well in it's first 6 months of operation but again, that aircraft can probably be better utilised on a different route. MAN - NAP was always an odd choice IMHO and struggled even in the busy summer months. Ironically, MAN - MAD would probably work well for them now there's no competition but I don't think they will explore that avenue again.
All this said, I can't help feeling that Monarch have lost their way a little. Once the airline who were proud to be different, they have effectively copied fellow LCC's, introducing charges, doing away with 'frills' left, right and centre and basically removing all the aspects of their product that made them so popular. It now seems that they're willing to be ruthless by axing routes they no longer deem worthwhile a-la WW or LS.
I'm not saying they should continue to operate loss-making routes to save face, or continue to serve free food and drink just to offer something different, but everything that made them stand out has now disappeared and they have become just another face in the low cost crowd. Any stability within the airline seems to have gone. Routes dropped, products dropped, charges increased and often far more expensive than their competitors, how much longer will their frequent fliers remain loyal? Are you listening Mr. Jeans??