They have different goals:

GrapheneOS wants to make a FOSS Android with the security model that makes it hard for any bad party to break into the phone.

LineageOS wants to make a FOSS Android that respects user's privacy first and foremost - it implements security as best as it can but the level of security protections differs on different supported devices.

Good news is that if you have a boot passphrase, it's security is somewhat close to GrapheneOS - differing in that third parties with local access to the device can still brute-force their access whereas with GrapheneOS they can't - unless they have access to hardware level attacks.

that is simply wrong.

GrapheneOS is both in terms of security and privacy the best but currently only supports pixel phones.

LineageOS is trying to support as many devices as possible still with lot of google connections and missing security updates.

>Good news is that if you have a boot passphrase, it's security is somewhat close to GrapheneOS

its not anywhere close https://grapheneos.org/features