Lucas is the massive elephant in the room and has been for some time. For some reason - probably because of his 'rise' to becoming a good player and the unwarranted abuse he took during that time - he's the only player absolutely immune to criticism from fans, which is nonsense.
However, he's been very poor all season. He picks up needless yellow cards and gives away free kicks in dangerous areas, he doesn't want to receive the ball from the defenders and play it out, he's constantly bypassed and doesn't cover enough ground, he's just useless at the moment.
He was looking like a very good player at one point, but it took him quite a long time to get there. He's regressed badly back to that same level, and we're paying for it. Alongside Skrtel, he's the immediate change that needs making to our team. It doesn't help that he's got Gerrard next to him (or vice versa) but together they're a catastrophe. Allen isn't naturally as defensive, but he can pass and he's comfortable in possession. Also, since Lucas hasn't done more than five minutes of defending all season, I'm not sure how he could be worse.
We're really suffering needlessly in games because of our refusal to adapt in midfield, and that's as a result of our lack of activity in the transfer market where we needed it most. We have four midfielders and three of them play every game, no matter how poor at least two of them inevitably are.
If our defenders are being punished(?) and rewarded for performances, then it needs to happen all over the pitch. Lucas to be dropped for a number of games, and I'd say the same for Gerrard if we had anyone on the bench in reserve.