These stats were taken in the middle of Alpha Season 3. The 4.1M total wallets are equivalent to users. But let's be conservative and say only half of those are real while the rest are bots. So in 2 years since launch, The Sandbox has ~2M total users.
Counting 2006 as Roblox's launch year, it has less than 2M users total if we just take their first 2 years since launch.
Comparing apples to apples, The Sandbox is actually ahead in terms of total users compared to Roblox in its 2 years since launch.
These stats from Alpha Season 3 are very good, particularly the average session length of 20 minutes.
It's still very early in the development of The Sandbox. A lot of things can change. But it's shaping up to be a viable storytelling platform for creators and brands alike.