I haven’t played Legend level, but all other levels. But the ODI, can and does go down if all of the ducks are in line. But then I’ve only seen a drop of 1 and a rare 2. If the Pandorans are active anywhere (attacking or building bases) the ODI doesn’t change, or could even go up a tick. I’ve done 2 citadels back to back and it doesn’t change, though at times it does.
We’ve got future changes coming to the ODI system, the enemy difficulty and Pandoran teach/evolution - though these are a little further out.
Clearing bases does actually reduce the ODI.
The current issue is that the ODI level is displayed as a percentage, but internally it’s a much larger number. Let’s say 0-10,000 as an example.
Clearing a base reduces the ODI, but sometimes not by enough for it to be visible as a whole percent on the ODI meter. So while you may not see the meter going down, you’re certainly reducing it and slowing the progress.
We are looking at changing this to make it more transparent, along with rebalancing the ODI reduction from clearing bases.]
And this is what the team is planning regarding ODI Replace ODI with survival of humanity | Voters | Phoenix Point