Iberia Gold is oneworld Sapphire, there is no such thing as AA Sapphire. AA Platinum is also oneworld Sapphire but aside from the standard oneworld benefits each provides different additional benefits.

You are correct that the earning on LAN when credited to Iberia is quite low compared to AA in discount economy, as LAN only earns 0.25/0.3/0.5 avios per mile depending on fare class compared to AA which earns 1 avios per mile plus a status bonus as they are a JV partner with BA/IB.

As LAN is also oneworld, you can credit their flights to any oneworld partner. However if you want to earn avios then you will need to credit the flights to your Iberia account or BAEC which has a similar earn on LAN.

You could credit the flight to LANpass or any other oneworld program, but then you would earn LANpass miles which cannot be transferred to avios.