WI is an example of how I backed a rubbish team to come good and they are. (Nothing to do with being an England fan before anyone else says owt about me with backing a *fit* England)
Simon Jones would certainly be a big improvement over Mahmood, I don't care what Simon Jones' record is like, he competed alright with Australia when he was fit against them - the best ODI batting lineup he'll face. England seem to have had at least two players out over the last year in ODIs, Flintoff was obviously completely out of touch when he came back and didn't have his bowling as you said, it was like of having some mickey mouse County Championship batsman there in the CT. England also had Tresco missing, Giles missing.
Whilst some of them may not be huge performers it's not one huge performance that generally wins you games in ODI cricket, it's having guys who can do a decent job from 1 to 11, if you have 10 overs that consistently go for another 15-20 runs than other teams and batting that contributes 15-20 runs less then you're in big trouble because of the nature of ODI games. I've no idea what'll happen with the wicket-keeping for England so that's one weakness that might remain.