Dovbyk is promising enough; he has been having good results last season in La Liga, but let's give him some times. Im sure he needs to slowly adapt to Serie A, but it'll be amazing if he delivers in his first season at Roma.
And last, hopefully, he can be a good replacement for Lukaku.
Dovbyk was the top scorer last season in La Liga. No one will doubt him to be one of the best strikers in Serie A. I think Dovbyk will need time to adapt to the style of play in Serie A. As far as I know Serie A has a very strong defense and has a pressing game like Atalanta, Inter Milan, Juventus and some other top teams. But overall Roma has won the jackpot by successfully getting Dovbyk. I am sure Roma will be able to improve their ranking and have a greater chance to enter the top 4 of Serie A this season.