Chelsea and Utd both wanted strikers this Summer, both Morata and Lukaku both appeared available
Utd went after Morata and Chelsea went after Lukaku. Utd were unable to agree a fee with Madrid which was probably down to the transfer of De Gea a few seasons ago, Chelsea couldn't agree a fee with Lukaku as they wasn't willing to pay the ridiculous agent fees. After failing for Morata, Utd bid for Lukaku and were happy to pay the agent fees, Chelsea then went after Morata, Madrid were much more open to selling him to Chelsea
Both teams ended with top class strikers who are both still relatively young. Morata fits into Chelsea's style more and Lukaku fits into Utd's team more and both strikers have made excellent starts
Don't see why there's anything else to argue about