I am sort of in the same boat, because the game gradually unlocks improved recipes, I end up rebuilding and rebuilding the factory over and over.

Going vertically doesn't really help, you have to re-plan and rebuild the layout every time some new technology unlocks. And (re)building in first person perspective, is rather fiddly. I doesn't help when better tools are only available in later tiers, when I get fed up rebuilding the factory over and over before I even reach it.

I am fine with iterating over designs, but I get fed up when I cannot create a modular design, change it once and update all instances of that design in on go. Instead I have to manually rebuild everything.

ShapeZ 2 also has a similar problem, but they at least offer copy&paste early in game.

For Satisfactory I am waiting for mods to hopefully make factory building less cumbersome.

I would prefer if Satisfactory would focus more on designing new factory modules and optimizing, scaling up existing ones. So a first milestone would be, create 30 iron plates per minute, next 30 iron plates/min and 30 iron rods/minute, then both of those and copper wires 30/minute. The maybe 120 plates, 30 rods and 30 wires, and so on and so forth. That way the player doesn't remove their factories, just and new ones or optimize/scale up existing ones. Together with a way to create, modify and instantiate blueprints, organized in a library, the boring and fiddly/gridy stuff of (re)building the factory is lessened. Also avoiding copy and pasting factories, by creating sub-designs and instantiating them would be great.