Seat maps 2 days out are not the most reliable indicator - there are too many variables on any flight to make an accurate assessment and that includes those who have paid for a seat finding the seat is out of service on the day of travel. My Athens to Heathrow flight last September showed only 1 row left in Club Europe 2 days before flying but during online check-in plenty of choices were open.

I successfully paid for and checked into a WTP seat a few months ago but it was at the airport that for “operational reasons” I (and others) were moved. We got compensation (and very quickly to be fair) but it is hard to predict.