I would say Jackson is not the best signing, but he is a good enough signing for Chelsea. Chelsea has too many strikers, so your suggestion is to sign a new striker may not be coming true. I'd rather recruit new defenders for Chelsea than strikers caused by chelsea conceded a lot of goals this season.
Jackson is a good striker no doubt because he has been doing well in an inconsistent club like Chelsea. Going top to the 11th position is a good effort to have been made by him in a seemingly competitive league like the Premier League. One thing that we should also look at is how the manager, Pochettino is strategically using them. Whether he's effectively placing him with a good support base or not. What Chelsea need is a strong defense, a collaborative midfield and a finisher. Someone like the Napoli star, Osimhen will be another good option beside Jackson.