Honestly, I think even if you only value getting "productive" things done and don't much value "unproductive" things, there's a lot of evidence that you can be more productive by being less productive where the mechanism of action is something like you burn out your capacity to do more work by consistently pushing yourself beyond what you can comfortably do to the point where you "burn out" and then find yourself unmotivated to do anything while you recover. A person can be sustainably more productive by giving themselves unproductive time to recover.
Meta note: that you got downvotes (I can surmise this from the number of votes and the total score) seems to suggest this is advice people don't want to hear, but maybe they need.
This idea is sort of sensible when looking at most people, who work for themselves or for relatively ineffective causes. In that case, the reduction in pay and productivity might be compensated by leisure time. Though people still actively prefer to work long hours in our economy and that needs to be explained.
However, we're Effective Altruists, not Most People. Our impacts are generally higher, whereas the value of our leisure is the same. Therefore, reducing our productivity is a very bad idea.