A playmaker is more important than a back-up striker IMO.
Kone, while terrible, is still a better option than Jelavic and Anichebe who were our main strikers before Rom was around. Other players like Naismith and Mirallas can do a job up top, thought it's not ideal.
Obviously, if Lukaku got injured for the season then it'd be worrying, but that applies for Coleman and either of our CBs (even after we sign a back up CB).
Meanwhile, I'd like us to sign a player than can help us get the best out of our players who like to get forward in Lukaku, Mirallas, Coleman, Deulofeu etc... as it's something we've been missing for a long time.