I think so, if Chelsea are serious about competing for the Premier League, they need a really top striker, Liam Delap is good, but i doubt he is the striker you go in with if you want to win the league, and as for Jackson, he is so inconsistent, he could play well in one game and perform at that level again a month later.
That said, what are the options in the market for them if they want to get a top striker, i can't think of any right now.
Chelsea will be competing for different trophies including the Champions League. They need to get a world class striker that will lead that attack. Any players could grow on a club and become extraordinary. Maybe Enzo Maresca wants to help Jackson and Delap develop to become world class. But this could be a very risky gambling since Jackson struggled to make an impact in Chelsea. My humble suggestion is that the club should just get one established striker and the available ones will serve as backups. Next season's schedule will be tight so they can get more players.
Irrespective of a midfielder's technical abilities, it would take a good striker to utilise his chances whenever he gets the opportunity near the goal, it is not about assist or positioning, Nicholas Jackson does all of these perfectly but he lack the ability to find the back of the net often times, which for me is the only thing missing in this Chelsea team hence the need to acquire another striker is inevitable to make his position highly competitive.