Someone who have 17000 steem power earn about 100 steem every day, that’s 700 per week
That sam person will be able to cash out 160 steem every week.
This is true ONLY if the hodler of the 17000 SP doesn't power down at all, from the moment you power down your earnings per day become less and less after each week, because you have less SP now, do you really expect someone who has 16840 SP to earn the same "interest" as someone who still has 17000 SP?
Also, as I already told you, each subsequent power down, powers down MORE SP than the previous one. I tried it and I know it. I suppose some earned interest is added to your power down amount as the time passes.
The power down is included in my calculation.
Someone who has 17000 SP will earn 700 per week minus the 160 that he powered down which means is balance will increase by 540 Steem power every week.
Someone who earn 16840 steem power will earn slightly less interest but I don’t see how this is relevant because he will also be able to cash out less steem.
Take for example someone who has 1700 SP . He will earn 70 steem per week and will be able to cash out 16 steem so his steem power will grow regardless.
The number of steem power someone have doesn't change the fact that the steem power balance is growing perpetualy even when cashing out every week.
There is a contradiction in your post. You said
"from the moment you power down your earnings per day become less and less after each week"
"each subsequent power down, powers down MORE SP than the previous one"
If your earnings per day decreases how can the amount of Steem power that you cash out increase?