Are you saying the star glaive isn't mandatory?
Per RAW, it is mandatory.
EDIT - The glaive is only mandatory if you're specifically taking the codex Autarch. GW have made a loop hole so that people can use their old models that aren't accounted for in the new codex. However, this also restricts some options.
This statement is incorrect. The flowchart explicitly states that you have to use the
codex datasheet for a unit
if such datasheet exists in the codex. So, for the HQ unit labelled "Autarch" you have to use the codex datasheet, there is no way around that. The only index datasheet that you can use purely from the Index is the "Autarch with Warp-jump generator", as such datasheet doesn't exist in the codex.
Next, the flowchart also states that you can still combine the codex datasheet with
wargear options from the corresponding datasheet in the Index. However, star glaive is not an
option - it's a built-in weapon and you can't just decide not to take it. You also can't have a shuriken pistol on the foot Autarch, for the same reason: it's not present in the codex datasheet, and in the index datasheet it's not an
option.
But you can take a power sword from the
"Wargear options" list in the Index and replace it with Shard of Anaris per standard codex rules for relics. You'll still have to pay for star glaive though.