Okay okay okay. So in my eyes, there's three major themes here: the value of an imperfect world, the freedom of not being the protagonist, and the lasting benefit of forming bonds.
As long as the Chainsaw Devil existed, Denji was never going to have peace. Time and time again, devils were going to come for him, to take Chainsaw's power for themselves and create their perfect world. The constant escalation resulted in Yoru's deathless world, where everyone would suffer forever. So in this new timeline, the Chainsaw Devil doesn't exist. Here, you can't simply remove everything you don't like. You have to accept that there are good movies AND bad movies.
Without Chainsaw, Makima can't pursue her perfect world, thus she's replaced with the more innocent and childish Nayuta. Without the possibility of a perfect world, she might accept that good movies and bad movies both exist. Here, she has the potential to grow up happy.
In the original timeline, Denji would've died in the Zombie fight if it wasn't for Pochita. But here he's instead rescued by Power. Power, who wasn't there in the original timeline. Power, who immediately takes Denji under her wing, though she initially hated humans. Because Power remembers, if only subconsciously, the bond they shared in the other world. And that bond is quickly rekindled, signified by Denji calling her the nickname, Powy. Despite not remembering him, Power and Nayuta still sense affection towards him. That bond wasn't wasted. It has value beyond death.
Finally, Denji and Asa. In this new timeline, neither of them are devils. They are both perfectly average people. They are both freed from their roles as protagonists. This of course means that their lives are forfeit. They will die some day, in some devil attack, as if it's nothing. Like so many other nameless background characters. Because everyone's lives are forfeit in a world where death exists. But we saw Yoru's deathless world, and it was endless suffering. So here they have the freedom to be unexceptional, and to die one day. An imperfect world, where death, and good and bad movies, all exist, forever.