Warning! This post contains SPOILERS for Rick and Morty Season 6, "Final DeSmithation."
Rick and Morty season 6 has been using Jerry to great effect with one new detail confirming just how much the Smiths' family dynamics have been changing over time. Across the board, every Smith family member has been evolving into new character spaces, growing beyond who they were in the first few seasons of Rick and Morty. While the same is true for Jerry, it should be noted that the new Jerry is very much the old Morty.
As seen in the premiere for Rick and Morty season 6, "Solaricks," it was proven that the original Jerry from the Cronenburg-reality had the potential to become much stronger and far more independent on his own than he ever was with his family. Likewise, "Bethic Twinstinct" sees Jerry choosing to take a degree more agency for himself in his marriage to Beth by leaving his "pillbug protocol" (even if the circumstances involving Space Beth were very bizarre). While Jerry is still the primary punching bag of the Smith Family, there have been signs that he's also growing into a new space with additional depth, even if that means filling a classic dynamic left by another character: his son Morty.
While Jerry has gone on adventures with Rick instead of Morty before, "Final DeSmithation" really hammers it home that Jerry has become a legitimate Morty replacement after he starts wearing Morty's clothes in this episode. Faced with a fortune cookie claiming that Jerry will have sex with his mother, Jerry freaks out and puts on Morty's classic yellow shirt and blue pants as an illogical attempt to trick the universe, hoping to avoid his disturbing fate. However, the subtextual point is hammered home: Jerry has now become who Morty used to be in the series (and it's actually pretty clever).
How Jerry's Morty Change Continues Season 6's Smith Family Fixes
Essentially, Jerry is now the old version of Morty from the first few seasons of Rick and Morty. He's not very helpful, and Rick can verbally and sometimes physically abuse Jerry just like he used to do with Morty before they started working on having more trust and respect in their relationship as partners. Jerry also has to be saved all the time, whereas Morty is far more capable now than he was in the past. As such, It’s a pretty smart method of giving Morty growth while still keeping a setup close to the original dynamic between Rick and Morty.
That being said, entering this classic dynamic with Rick is still growth for Jerry as well. It allows him to have a far greater role in the show that goes beyond simply being the "disapproving and weak-willed dad", thereby making him more interesting and dimensional as the series continues. Ultimately, it makes sense that Jerry would need to have growth, just like any other member of the Smith family, especially considering Rick and Morty season 6 has already made fun of the earlier seasons' family dynamics which have now become outdated.