I think your point is good. If a 4% rate work works out to pay for your lifetime reducing that would leave money behind. So you would not included the SS in your calculation and still withdraw 4% of your investments, as I understand you? This is where I tend to land too. But just want to make sure this is how most people deal with it.
what does your retirement plan say?
You need to plan not only until both claim, but also what happens after "first to pass" !
while we haven't come close to 4% (more like 2% or less) before the first SS, we have a plan
--if I pass first, then pension drops to 50% (the max I could set it for)
--my PIA is the lower (but not that much lower) but I am older
So: if I pass first, SO goes on surviving spouse (my SS, which is starting first payment this month); then there would have to be something to make up the difference
What makes up the difference is savings (able to make up difference until they get their higher age-70 payout). If I'm gone after we both are claiming, pension still drops by half, but
part of the payments that are received when we both are collecting are saved for future offset of the difference, so that SO won't suffer a drop in living. {....and if SO passes first, I would receive the higher SS and (potentially) a step up in pension. The age difference, plus that I'm male, makes that unlikely}