this is 100% correct -- the only remotely workable options at this point are Biden or Harris, and reaching closure about this and ending the discussion as soon as possible is the most important thing that needs to happen
At some rapidly approaching point it will be less important whether Biden carries on or steps down than it will be to simply stop the speculation. Pick one. "Final answer: I'm running / I am stepping down." The worst outcome is neither Biden nor Harris; the worst outcome is debating it for 100 days.
Like her or not, if someone else needs to step in for Biden next summer (hopefully not), anyone *but* the sitting VP will read like an admission of failure and bad judgment back in 2016 -- a liability that will hobble any replacement.
("Biden's old" is not about Biden, it's anxiety about Harris.)