Lots of great points.
I’m not at an unlimited vacation company anymore, but when I was the one thing I liked most about it was not the big lump sums of vacation that I could potentially take, but the smaller day or half day times off. I felt so much less pressure when taking parts of days off for errands or a random day off to deal with anything. For me, the unlimited time was best for short leave rather then bigger time off. My day to day pressures of work vs non-work stuff was less compared to previous companies.
I appreciate the accounting of large chunks of time off because as you say, it alleviates a bunch of ambiguity that can cause social pressures. There’s already enough of that with a set amount of vacation time. But it’d be nice to have a block amount for big vacations along with a policy of “unlimited” small time off.