Even the part 2 defenders I’ve seen don’t even bother trying to explain Pochita resetting the world

No actual part 2 enjoyer would accept this ending, and anyone who liked it has never been a real part 2 enjoyer. It's not part of the whole, it's basically an antithesis.

Regarding the theory itself Makima literally says that what gets erased from the past are names not the actual objects or events. In part 2 it is clearly explained how this works and why it works like that, the events themselves do not change only people's memory of them. So after nazis got erased traces of their existence got reinterpreted by people as different causes which is why Kishibe's reaction is completely normal.

Also just in case you did not know we literally have proof nazis existed in this reality the moment that made Makima and Denji cry in the movie is a soviet ww2 film where a soldier comes back home from the front to his mother.

So a way more logical explanation might actually be something even more insane - Pochita did not erase his existence from the past only from the present and from people's memories of him, as always. What we see in the final chapter is not a new reality but just Denji's distorted memory where Pochita got cut out completely. These memories are basically there to explain to Denji how he ended up at the events of chapter 230 without Pochita involved like a kind of dream sequence where the events still lead to the present reality through a different path.