To be honest, this arguement is poorly founded and absolutely ridiculous.
The reason no one steps up and makes it from the Championship in the premiership is simple. All the better lower league players get brought into the top 3 or 4 championship teams, and get promoted. They then have a great half season/season and a bigger club comes in for them, or their team get relegated, and the player moves onto another premiership team.
The second reason it is rare to see is because Championship and Lower League teams always ask way over the odds for the players in their team. The result is premiership teams buy players when young and add the finishing touches, buy abroad, or invest only when the player is proven.
The one exception to this rule is a promoted side, who will look to strengthen their team by buying players from the teams around them who didn't go up.
Arguing that no player ever gets bought by a prem side and then makes it, where as players can transition well is nothing short of utter bollocks. It's not about buying and doing well, it's simply about players being able to transition, and many a player is able to do that.
When you look beyond the mighty RFC, you have players like Dawson, Defoe, Carrick (both of whom had played in the prem, but were bought from the championship), Andy Johnson, Lescott, Carson, Dyer, Young, Walcott, Robbie Keane, Bellamy, Jerome, McShefferey, Ashton, Kenwyne Jones, Jenas, Simon Davies, Etherington, Crouch, Jagielka, Koumas, Jason Roberts, Upson, Green, Reo-Cocker, Anton Ferdinand, Zamora, Nolan, and god only knows how many more have made that transition in the last 5 or so years..... Except Keane and Bellamy - they were tongue in cheek as they've been around a while now, but they still made that step up.
To say lower league players won't make that step up, unless in a promoted team is a ridiculous comment, as they still have to step up if promoted and a lot of players do make that transition rather well.
Granted, it is harder now, but if you look back in time, that was the route nearly every player took. Despite the fashion to go abroad because it is cheaper, lower league players can still make the transition and to make a comment like they won't unless they are promoted is outrageous.
I would be happy to see us go after a number of lower league players - Watson is one of them, and I believe, especially with Coppell at the healm, they will be able to make that step.