but how would a person on a single-user fediverse instance be any more censored than a NOSTR user? Isn’t the biggest difference in those two scenarios if the “node” is push or pull?

No. When you push a post on nostr you push it to multiple relays at the same time. And when you read other's post you request for their content from multiple relays. For example I post the following controversial topic

I think children should have to wait til they are 18 to take puberty blockers due to this new study that was just released.

And to the following relays,

• relay a
• relay b
• relay c

User WiggleSoft is following me and listens to relay a and c and g.

Relay c decides they don't agree with my take on puberty blockers and think it should be given like skittles to 11 year olds. They think that science journal is fascist. They block me on relay c.

WiggleSoft ask for my post from relay a and c. Relay c returns nothing because they hate me. relay a does not care.

Me and wigleSoft continue our conversation on relay a like nothing ever happened.

relay c does not own my identity. They can not tell other users that they are not allowed to read my content.

That is all nostr is.

It takes identify management away from admins so you can use multiple backends for the same user.

It makes it more like everyone is running on their own instance.