I'm sorry, but no. This is not a Spa problem. A crash like this could have happened at a large number of circuits in these conditions.
Remember that wet Brazil GP a few years ago when Kimi spun on the start finish straight, ending up stationary at a 90 degree angle to the track? Could have easily been fatal had he been hit. Same possibility at Baku (even in the dry because of the blind corners), Monza, ...
It's basically impossible the run modern open seaters in these conditions because of all the aero downforce and thus spray. That's the discussion to have imo.
Not much to say aside from agreeing with Lance here. Motorsports will always be high risk but it's a matter of mitigation. It's insane that they resumed the race in those conditions and it's insane that no meaningful changes have been made to these corners since Anthoine's death. There have been other legendary corners at Spa that were revised due to driver deaths, so something new needs to be considered here. I don't know if the 1994 chicane layout makes a ton of sense, but they need to find something.
Edit: After reading more, I really also want to emphasize just how badly race control fucked up here. Safety car for 15 minutes in cold weather and driving rain...and then giving the green light with a single lap to end the race? Anyone that thinks that is a reasonable idea is insane. There is absolutely no time for tires to come to temperature and even if there was, I still feel that racing Spa in significant rain/spray conditions is just dumb.
They absolutely shouldn't have been racing in those conditions, especially doing a restart and dash to the end - it was a recipe for a crash.
Ahead of the fatal crash you can see a car bounce back onto the track after crashing in the corner. Fortunately, that car could still move and the driver zipped it back off track, otherwise he likely would have been hit there.
While this can happen at many tracks, the speed and layout-related visibility issues at Spa make it much more dangerous than other circuits