Firstly, I think that both Williams and Hughes have looked below par especially when playing centrally in a conventional 2 man midfield, however Williams has looked better in a 3 and I am fairly confident that given the opportunity Hughes would perform better and influence the game more in a similar role. For me neither player is strong enough defensively or possess the physical strength required to play in a 2 man midfield.
IMO Williams playing style is not suited to the hustle and bustle of British football unless he can operate as a deep lying playmaker in a 3 man midfield, otherwise for me he is more suited to the continental style of football, he is a technically gifted player, who has decent vision and a good range of passing and I honestly believe he would do well in any of the French, Italian or Spanish leagues, although I am talking mid table to lower half sides, I am in no way saying he could play for Madrid, Juve or Barca.
As for Hughes, he needs to bulk up, as at present he is too lightweight to play centrally in a 4 man midfield, but neither is he a wideman, so he needs to add more steel to his game before he can be a truly effective central midfielder in the English game. But he would be very effective in the 3 man midfield that CL has been operating with in some of the recent away games.