That actually opens up new questions in my mind. I was going to say that Duplicati does x amount for validation and I think that can be changed (I briefly came across that before but others here would know better about that) but really that should be able to be done in memory only. I think that does write to disk but could be wrong.
Perhaps various ideas here might be of help for different settings Does duplicati download any data? - #13 by JonMikelV
You could lower the amount as well by avoiding backing up larger files that won’t ever change and just back them up once manually without Duplicati.