Steering away from the argument of whether Lucas was the "most to blame" for the goal - it's not the fact that he lost the ball; it's the way he lost it. Mistakes like that shouldn't be happening for professional footballers. I think that part of it is a fair criticism.
Indeed they shouldn't. And to note that he got dispossessed from behind with a simple toe-poke, and to criticize him for it would be both fair and accurate.
A few others and I immediately stated that.
Now, has Lucas had many of those in the last 2 or 3 seasons? I think not. Did he use to have a few too many of those too often 'back in the day'? Yes, yes he did.
Is Lucas "mentally slow" as "evidenced" by his "habit" of being caught in possession? No. In fact, hell no.
Did Lucas cost us WHU's goal? No, he did not.
Did Lucas's mistake "lead directly" to WHU's goal. No. Hell no!
Now, having established that Lucas made a major mistake, and that he should see to it that he doesn't do it again, one can then move to consideration of similar (even worse, in fact) gratuitous possession-losing-mistakes by other players.