I think the real weakness of DD and SoJ is the big final case twists are final case twists/reveals rather than being the climax of a full game story that come to fruition in the final case.
In AA1 DL-6 was introduced in case 2 via Maya's family and Mia's motives as a lawyer, so as well as the internal twists and Edgeworth's characters arc 1-4 serves to provide some answers to those questions.
In JFA the magatama is introduced in case 2 then subverted in finale, serving as a thematic payoff.
In TT we finally learn more about Maya's mother, resolving a mystery set up in 1-2, and Dahlia is involved 3/5 cases, so the finale is the conclusion to years of Fay family drama we have been invested in.
Both the Investigations games have an overarching mystery/conspiracy (1 has the clear throughline of who broke into Edgeworth's office and why, 2 is less apparent in the early cases but multiple individuals from those cases come back and have their earlier actions relevant in the climax).
GAAC was clearly written as a 2 game storyline and multiple elements set up in game 1 don't pay off until part 2.
AA4 the final case is where we learn how Phoenix came to be disbarred and adopt Trucy, a question established in the first case of the game.
But as much as I love the phantom twist and the Blackquill reveals in DD there's really little set up, we know that Blackquill is in prison for something but it is only retroactively that we have a reason to care. You could play case 4/5 in isolation and get the same experience, same with case 5 of SoJ. They aren't bad cases but they don't deliver a payoff the whole game in the same way.
