Lach, I fully agree with the fundamental point of your argument, that Leiva is a much improved player who with a bit of luck (he's already proven he has the dedication of mind), could be a top, top player by the age of 26.
The abuse he received was unfair given his age and background. The fact he's in the Brazil squad speaks volumes. The fact he was their captain at U19 level indicates his potential. He deserves every chance and I feel your comparison almost sells him a little short. As others have mentioned, he reminds me more of Busquets or Makele in what he does and given his incredible dedication to LFC I'd have him over any other player in his position in the Premier League.
Give the lad more time.