TBF on the 12 thing who could you argue has been really hard done by in terms of selection? In the past like 10 years at least
Tomkins, Williams, Redpath, Harris.
Devoto would be in the list if he'd managed to put together 2 consecutive injury-free years.
And is it so much "trying to find the next Manu" as "Manu is still plenty good enough when fit, whilst Farrell is either 10 or 12".
The only example I can really agree with (that I can think of off-hand) "trying to find the next Manu" is trying to shoehorn Lawrence into the 12 shirt, where we can show off his weaknesses, and ignore his strengths.
But then, I've always said that one of the hardest things for an England coach is to pick which players to show faith in, and then to show that faith through a run of poor form. Fans and Press want selection based on form (meaning about 6 weeks worth) - which means at least half the team to be changed for each international window; and no consistency ever built, and no players ever feeling comfortable at international level, and able to take a risk - as pretty much any risk that doesn't come off will see them crucified in the press and dropped for the next bright-and-shiny.
If you've only got 2-4 options, grading them into a pecking order must be pretty easy. England typically have 10 or so options, covering the same range of quality - so grading them is harder, resisting calls to change them is harder, investing 50 caps worth of experience is harder; and helping any of them actually fulfil their potential is harder.
Let's face it; the 4 I listed above (tongue in cheek), only Redpath could have expected more than a handful of caps for England. All bar maybe Williams (enforced by injury) have picked up enough caps to be comfortable at international level - a height they likely wouldn't have reached with England.