But why do I say 20% reduction in work?
Bugfixes and features that get fixed/finished on Fridays will ship 3 days later. Do your average lead time increases by >0.5 days. This impacts anyone relying on you, too. So if this happens org wide then features and projects may ship days to weeks later.
Oh and what are you doing on Fridays then? Less relevant work? If you stick with priorities then you are just queuing up more changes for Mondays, leading to nice higher risk deploy Monday. You simply can't gain stability with skipped Friday deploys without changing / ignoring work priorities for Fridays.
So yes, this should be comparable to such a reduction.
Oh, and Friday deploys ruin your weekend? That means you have really high detection and mitigation time. With 1h detection time and 2h recovery I could still with low risk deploy Fridays, 5PM, wait 1h and enjoy a weekend after wrapping up my work.
I have always shipped on Fridays. It never ruined my weekend. Even though I did have a few fun screwups (which sometimes required help from my coworkers).