Not sure why this is still a debate. Lukaku might not be the biggest problem but he is not the solution and every season he's around we are one step away from finding that solution. Look around at the teams regularly challenging and winning trophies and see who they have as strikers. Barcelona have had Messi, Neymar and suarez, real have had Ronaldo, atletico have had griezmann and Costa, City with Aguero and the united of old had Rooney, van Persie and Ronaldo. Lukaku is simply not in that caliber at the most important position in attack.
I'm not even sure he's better than vardy from the season Leicester won the league.