I thought server optimizations were always targeted for around 1.20.
1.18 was the initial content patch.
1.19 was focused on materia crafting, fixing the battle system, more content and beginning job adjustments (now just to be outlined, and implemented in 1.20).
1.20 was going to be jobs + server changes. First priority was fixing hella broken game mechanics, then after that hella broken infrastructure.
XI Wiki



