The problem is that they pick an ODI squad and then play T20s with it. Obviously, most countries tend to do this on tour, but for England this methodology is completely flawed because England's ODI team isn't exactly a champion at its chosen format. What they should do is pick a squad specifically for the one or two T20s they play in a tour and then find a way to make an ODI team from that.
Before you ask, I'm not sure if I'm joking or not.
It's hard to say really what direction England need to take because they seem to take turns in stumbling around all departments. I doubt they have the resources to make a batting dreadnought like South Africa, but they don't have express pacemen or arcane spinners either. Maybe they just need to find their strength and embrace the direction it takes them in. Suffice to say, no team should be planning on chasing 240; the batsmen might as well just take the time in the middle.