I agree and have a slightly different view at the same time on Allen. I certainly agree that there's something wrong when he and Lucas play together. I would also say there's a problem when Allen and Gerrard play together, especially when Gerrard plays in an advanced role.
I think the problem stems from playing a 3 man midfield with Gerrard in an advanced postion. We become very spread out and stretched which leaves huge gaps for the opposition midfield and forwads to exploit. I wish I could do pictures to illustrate my point.
have a look at this video and pause it at 1:24.
Look at the state we're in. Gerrard has lost the ball and is walking. There's a huge space through the centre and our right flank. The central defenders aren't aren't even in the shot. There is no sign of Lucas in this instance. His effort to tackle left me raging afterwards by the way. My point is that we are all over the place, no shape and not high enough. No where near tight enough. The distance between the forward line and our defense is far too great. We invite problems like this and any defensive midfielder would look rubbish when exposed like this.