I think part of the issue is that lack of percentage bonuses. Production tends to ramp up quickly as your city is growing and you set builders to get your industrial complex and mines/lumbermills operational. But then, production mostly plateaus....with only industrial districts from other cities adding anything. Even in Civ 5 you had windmills and factories to give a +35% bonus to your existing hammers. The end game hammer costs I think assume your production gets scaling, but it doesn't scale that much after the midgame.
Some easy fixes:
1. Districts only scale per city, however what even is the logic for scaling districts other than they're too powerful?
2. No scaling but there's an economic penalty for building them. This makes sense, just have an upkeep for districts based on how many you have plus buildings in them
3. Keep scaling the way it is but allow builders to hurry them up
If you're going for the science victory, getting Carl Sagan as a great scientist helps an immense amount, as his ability is to give you a free Spaceship module. But, I think he might be random like the rest of the great people, so if you're unlucky you won't get him and have to spend the extra 30 turns or so.
And yeah, factories are immensely important. I've found that I like Japan a lot for peaceful games because they have a unique improvement to factories and better districts.
And in the end i was building mars project parts in 8-9 turns. Not bad.
The first thing a new city should build is likely to be a district, the second thing a new city may build may be its second district and the third thing may be the third district depending how quick population growth is.