Quote Originally Posted by KarstenS View Post
As far I remember, the ex versions were premade right at that start. Solo queue got introduced at a later time together with echo buff.
The original three EX primals were initially available via the DF. It wasn't until Leviathan EX that EX primals were kept outside of the DF for a period of time. Yoshi-P talked about the reasoning for the change a bit in an interview (I thought it was in a Live Letter, but I just looked through the ones around that time and didn't find the reference).

You can essentially confirm this in the Patch 2.2 notes. Echo was added to the duties at this time, but there was no change mentioned about being able to solo queue for them because you could already do so.