I really wanted to enjoy Satisfactory, but I found that a first-person perspective just plain sucks for factory building. I haven't played it in a long time though, so maybe they've made some improvements?

I ended up enjoying Dyson Sphere Program so much more. It's the "Factorio but with a third dimension" that I really wanted.

About 40 hours into my save, I realized I could use the "foundation" blocks as a way to organize the factory since everything snaps to a grid when you place stuff on top of it. There's also a "hoverpack" item in late-game + some folks use fly-mods. I haven't gotten that far, so I end up using lookout towers + foundations to get things neatly arranged.

Oh, did they add snapping to a grid when building on foundations? There wasn't a snapping option when I played. At best, you could align one building to be directly adjacent to another, but that didn't help when making belts.

They made significant improvements to building in the Updates 4 and 5 iirc. Some basic bulk creation options, toggleable clipping, global grid alignment, etc. Coffeestain is doing a really good job of taking a good game and giving it the polish and QOL features that should turn it into a great game when it exits Early Access.

Did they ever improve the belt system? I played it in early access and it was a chore to get belts to tile reasonably and be able to manifold off of them to feed more than one factory

They continue to improve the building and placement across the board, so that really depends on when you were playing. It remains in early access but its very solid at this point.

Last I played was July 2020, about a month after release

Coffee Stain (Satisfactory Dev) made improvement with the games. They are on Update #5 now and soon will be releasing Update #6. Try it out now to see if they fix it.