I think its simple - If the team does well, Lucas does well; if the team plays shite, he plays shite.
That seems true and you could derive from that that Lucas will never be the type of player that steps up when we need a leader or be a key component of a title winning side.
However, there's more to it than that. Instead of just stating observations like this we need to analyse and calculate why that might be the case, and for me the reason is obvious. Like others have said earlier in the thread, there was no movement in front of Lucas. If that's the case then it doesn't matter whether you're Andrea Pirlo or Robbie Savage, you're not going to be effective and you're not going to stand out when attempting passes.
Even Xabi Alonso was 'culpable' of this. For much of his two mediocre (ahem) seasons he was willing the team on by attempting passes to good positions in space, but because of the lack of movement and ideas from the forward players, they failed and Xabi was labelled as being poor. A pass can only be as good as the player on the end of it.
This is, in my opinion, part of the reason why Rafa wanted to sell Xabi last summer. As good as he was, Xabi made our play too predictable at times. He passed on to players in better positions but never followed up and supported them in attack. He didn't attempt to dribble with the ball either. Due to that, his ability was nullified if the players in front of him weren't performing well. With a player like Aquilani, or potentially Lucas, they might not be as good at passing, but they can still do what Xabi does to a limited standard. However, on top of that, they provide further options in being able to move forward and support the attack, and therefore creating more space for others, or by carrying the ball forward towards the box. Xabi either couldn't or wasn't trusted by Rafa to do so.
I think that's why Rafa has faith in Lucas, and it also explains why Lucas isn't standing out. He did attempt forward passes to players against Villa but very few passes are going to be successful unless our players are constantly moving and attempting to confuse opposition defenders. Added to that, whenever Lucas did attempt to move forward the ball was never played back to him, as HBHR points out. Until our own players have a little more faith in Lucas, and until they help him by being less static, he's never going to succeed. And that's not his fault.