When Jason connected to Sonny, he was still a Quartermain, even though after his brain damage he was happier with Sonny who accepted him for who he was at that time. The pain the Quartermaines exhibited over the extreme change in his personality was too much for him. Sonny became his safe place and they became tight.
But the Quartermaines were still there and Jason still had scenes with them. Jason's relationship with Robin flourished, and there was his friendship with Carly and helping her with baby Michael.
Dex has his romance with Joss, working for Sonny and his romance with Joss and working for Sonny.
Dex has no secondary relationships nor storylines which limits his storyline to Sonny and Joss. And as I say with alarming frequency, a romance does not a storyline or character make.
Dex is in desperate need of secondary relationships AND a fleshed out backstory. That was the primary problem with Cody and Austin -- the show HINTED at backstories and secondary relationships, but never did anything with them FOR YEARS! They finally cut Austin loose and are trying to get movement with Cody from a complete stop.
If Dex is going to work as Sonny's right hand man/Jason replacement and a good romantic partner for Joss, there has to be more to the character that being Sonny's Go-fer and Joss's snugglebunny.
Karen L.