All very disappointing.
I hope that they do offer a free race at some point, as Lewis has requested.
Comparing Fuji to Spa is a non starter, one has large run off areas and no dangerous corners, the other is a very dangerous track in heavy rain.
At no point did the drivers think that the race was safe to start during the heavy rain. So just saying that they should have gone ahead and tried to clear the track is a non starter. The rain was falling fast enough to mean that the track would always have put up too much spray and there were areas where there would always be dangerous aquaplaning (i.e. unpredictable due to rain rate, drainage, speed of entry etc).
To run the race on Monday would require a few changes:
1. Monday would need to have been planned in advance as a test / spare race day (need safety team, marshals, film crews, FIA, circuit operators, teams and hopefully fans).
2. The following weekend would not be another race event.
3. What ever FIA rules that need to be changed to allow this, would need to have been changed.
Some other possible options are:
1. Given that Spa is an outlier circuit (weather and dangerous track) it needs more and better planning to make it viable on more occasions.
2. We just accept that one in 40 races (made up number!) at Spa need to be cancelled, and that a race is re organised on a weekend allocated for possible delayed race.
3. Or we accept that the race is just lost from that calendar year.