It's not his scoring record. It's his general play. You can be a less than one in two striker and still be a great player. Drogba, Raul, Rooney and I can go on. Just take five minutes out and have a look at Drogba's technique - the way he controlled the ball with a single touch, his movement in the box, his use of his strength, his ability to draw a foul (and spend five minutes rolling around) or his ability to find Lampard or someone else. Literally every memorable moment Chelsea had from 2005-2014 involved Drogba. As for Van Persie, well he was perhaps the most technically accomplished striker in the last decade not named Messi.
Lukaku is a good player. Too good for Everton, good enough for a top six team but perhaps not quite good enough for a title winning side. He doesn't use his strength well enough. The way he's built he could flatten most defenders, yet we never see that. The ball bounces off him like a baby elephant far too often. Take two moment from yesterday - First, Sanchez played him through, he took a good first touch with a defender on him, his second touch negated the whole move. With Aguero that would have ended up testing the keeper at the very least. In a high pressure game when three points are on the line or a trophy up for grabs taking that chance might well be the difference between winning and losing.
Second, Pogba's long pass to Mata was cushioned by a great first touch and the second a pass to Sanchez who drew a foul for the penalty. Can anyone on this board honestly say he/she would expect Lukaku to complete that move with the finesse Mata showed?
No matter what clowns on this forum think of Juan Mata, his technique alone makes him eligible for the top level. Lukaku is far far away from the level of Harry Kane or Aguero or Greizmann and any other striker for a top team. Again, it's not his scoring record. Both Vardy and Firmino have identical records. The latter has an excellent touch and awareness. And no, I don't want him to 'fail' at United. If anything I'm more than happy to be proved wrong.