Requirements for 7* Chimera

I have 4 Rebel ships 7* (Ghost, Biggs, wedge, Cassian’s) and a 7* home one. I’m 30 shards off getting Phantom to 7* - On the requirements section of the final tier of the Chimera event it says I only have 3/6 ships collected??? I’m nowhere near with Bistan’s (even so 3/6 makes no sense) there’s only Phantom and Bistan’s I don’t have maxed? So again 3/6!?

I guess my question ultimately is do you need every Rebel ship 7* to complete the event and unlock the 7* Chimera? And can anyone explain where the heck 3/6 comes from!?