I don't withdraw from SN but if my balance ever got high enough I would withdraw some. I think the most sustainable model is a hybrid of a circular economy and external revenue sources (ads, promoted posts, job postings) that allows SN to generate revenue, share rewards with users. I don't think there is anything wrong with people taking the time and effort to create content and engage reaping some of the reward for that and withdrawing some sats to their savings.

What if the criteria for withdraw of rewarded sats was above a certain level? Say 10k sats.

You could split deposited sats and rewarded sats. Obviously deposited sats would always be available for withdraw but rewarded sats need to meet a threshold to be removed from SN.