CIG also gave other stats for 2020 in the December letter:My bad, I've missed the title of the steam chart and though it was daily players.
CR said the max unique players for one day in 2020 was 100 K. If those players were evenly distributed throughout the day (never the case but not enough data to extrapolate, I wonder what the peak player is) and played 1 hour (don't know either the average time) each, it's 4K concurrent players average for the best day in 2020.
You are correct, with the last numbers given by CR in 2020, SC alpha is certainly below the ED alpha.
- Total playtime = 26,576,364h
- Average daily playtime per player = 2h25m
- Average daily unique players = 30,000
- And a graph for Daily Active Users (seems to be equivalent to Daily Unique Players):
The graph shows an 80% drop in playerbase from the record high (100k unique daily players, on a day during Invictus) to 45-50 days later (~20k unique daily players).
Interestingly, and perhaps coincidentally, Elite Dangerous on Steam had a 78% drop in peak concurrent players from Odyssey launch-week (28,923) to week-including 22nd July (6,367):

From that data we know that the average concurrent for the whole year is around 3,100 players (30000x2.5÷24 = 3125), which is considerably lower than the concurrent that other space games get even during their low months. There was a meme for that too:
