In terms of real life battery usage, if you are aiming for 8 - 10 hrs then the MSI Prestige cannot be considered in that list. It's battery hungry. You will probably not get more than 4 - 5 hours max on any laptop with a dedicated graphics card.
The X1 Carbon on the other hand will easily give you about 7 hours on there similar to the Dell XPS 13. Their U processors are less power hungry but have nice turbo boost clocks for heavy loads, the x1 carbon gen 7 all come with 16gb ram afaik.
Carbon Pros: good keyboard, good battery, decent processor, nvme ssd boot drives
Cons: fans are known to kick in at weird times even under light loads (they're quiet which is nice but still), complaints about glare on the display.
(I'm currently thinking of buying either the x1 carbon gen 7 or gen 6 and someone shared this link with me to get it in the 1200 USD budget
Zenbook Duo thoughts, you would probably be paying for the idea of two screens more than the functionality, the second display combined would make a significant difference in battery usage.
If you can do without a discrete gaming graphics card, then opt for a business laptop for better build quality, processing power and lightweight.