And even these days the typical investor probably uses a financial advisor, who would do such fund reallocation, even if they don't use target date funds explicitly (which they should).
Do they really? When I've looked around at financial advisors they've wanted at least several percent annually of AUM, which, to my mind, is just insane.
For this hypothetical, I don't think it makes sense to consider anything but a typical 401k investor that only invests in the sp500. Thats all that we're tracking here.