Maybe. Factorio does a great job of putting out releases and sharing details about what they are working on and you would have thought they were evil incarnate after they recently said they had to raise their price by $5 to keep up with inflation.
People are fickle and hindsight isnt always so clear.
I don’t know for sure but 3.5M lifetime sales times 30 is $105M*70% is $73.5M, they have around 30 employees, maybe they pay $200K a year, so that’s $36M over 6 years, netting them $37.5M. I could be way off though.
The game wasn't always at $30. I saw it for $20 a few years ago (regular price) and I believe it was even lower before, like $15, but I'm not sure.
There is also a Nintendo Switch release, so they will have to pay for the Dev-Kit's and licenses which are not cheap. Not as expensive as in the 80's, 90's, early 2000's where a single Dev-Kit could be six figures, but still a significant expense for a indie studio.
So we are already a little bit off from the numbers you posted. I assume, the 30% you cut off is for taxes. Good idea, but Steam and all other platforms where the game is sold also want a piece of the cake. I don't know the numbers for other platforms, but Steam takes 30% of the listed price.
So even with a $30 price tag on Steam, they get $21 after commission. An that is pre-tax... They need to buy hardware for their developers, rent an office, pay developers and so on. So even the founders are not getting rich. A "boring" job in business software can make you more.
People are fickle and hindsight isnt always so clear.