Both Cole and Corbisiero start a hell of a lot, and play at least 30mins per week. Don't know where you get Lawes from; Farrell not starting 10 is clutching at straws, considering he did all of 2011 until about October, and now rotates there while starting almost every game anyway.
There's not a yawning chasm at fly half. There's two or three spots to fill, and off the top of my head I can throw down four names of fly halves who start regularly in the Premiership, are young enough, are English, and are playing well. Not to mention several others who are old, or who play abroad. Clegg (and George Ford and anyone else) are both young and shouldn't be thrown into the mix just because of their age.
People must not forget that the England squad for this 6N needs to be a group of players that can be built into a top class team over 4 years with the help of later additions. That does not mean picking an U23s side based on how good we think they may be in 4 years, it does mean picking a squad devoid of players who won't be around in 4 years time and are taking up spaces.