Siwa only guarantees that there might be some form of life, maybe. It does take a lot of rerolling or luck if you want specific parameters like a lot of ruins on a breathable world.
For example: Some players are getting megacity planets with 5B+ initial population. As it stands, if you wanted to play a world like this you would either need to ask for a save file (and use the first person's game settings) or spend potentially hours rerolling trying to get perfect parameters. I've personally spent a few hours over multiple play-throughs rerolling to get worlds with A) large populations (for ruins), B) open air farming, and C) hostile aliens.
However, given how intricately designed and interconnected the parameters of the planet generation are though, I imagine it might be difficult to disentangle it. After all, trying to set a slider for hostile aliens in the biosphere phase when you already rolled up a lifeless moon might cause issues.
My suggestion would honestly be to go in a direction somewhat like Dwarf Fortress. Offer an alternative map generation option where you only have one menu, set desired parameters and weights, and the game automatically rerolls maps until it gets one that fits.