[Ingaz]

You're correct: omz adds not a lot to vanilla zsh.

It consists of: - collection of plugins/themes - auto update - way to customize them

Everything could be done directly in .zshrc, it's just a bit more convinient

[sshine]

I used zsh for a few years before oh-my-zsh became a thing.

I have to admit that I don't find it more convenient.

It takes an ecosystem where things have a way of working, and establishes new conventions on top of those using a new set of environment variables. So if you know zsh, you don't know oh-my-zsh.

A vanilla zsh will feel very bare.

A vanilla oh-my-zsh will feel very feature rich.

If you end up configuring zsh anyways, I don't see the point at all.