Both games are more of the category easy to learn, harder to master.
Stellaris is really accessible, after 1-2 hours you get how to play it, but you will find nice details side quests ect even 100hours in.
(A lot also depend on your created races ethics, for example a religious one might declare a falling star a sign of propserity or a war start, a industrial one might just harvest the ressources it contained .) )
What I really like about factorio is the similarities to legacy code. (especially in multi-player It actually makes non IT people understand how it is created.
Why is this part of the factory designed like shit?
Well we needed a quick solution, and look you only have to haul a few ressources every few minutes manually.
Ugh, can't we just rebuild that part better?
Sure, but we need the ammo for the outer perimeter now, if you somehow disturb it for a few minutes we will loose the outpost.
Grumbeling ok once we get drones, we will patch a resource supply in somehow.
Sound familiar to some software projects?