There are some geometry and rate problems such as multiplexing resources on a belt.

Honestly, I think the feeling of not wanting to have to bust out a spreadsheet to play a video game is entirely reasonable and shouldn't be downvoted. but this is HN in 2023, so he'll get downvoted, while, who does use a spreadsheet will get downvoted when I admit that the spreadsheet I use is from Microsoft. =)

You don't have to though. Base facrorio does not require any spreadsheets or math (other than production lines for efficiency, but that's kind of the nature of the game.)

It's a mod, and so not required and already something you decided to optionally add to your game.

And for production lines, you have plenty of mods that can do the math for you : Helmod / Factory Planner, Actual Craft Time, Rate Calculator...