300 people can do more then 1 act in 1 month. You can make all of act 1, 2 in 1 month if work flow is done correctly. I made a 50 map pathfinder campaign [urgir, Mandev, custom city 4x size of bg3, level 16, the entirety of the land of mammoths, in less then 2 weeks myself using solasta game engine DM maker. People think it's hard... it's not. Only reason there is so much missing content is because the devs where lazy to complete it.
Lazy to complete it? Are you okay, lad? You've said more than enough to ensure me that you've no idea what you're talking about.
They were forced to cut content, at least because they were runing out of time, not because they are lazy, jeez...I assure you, Larian couldn't afford lazines during BG3 development, too much at stake, BG3 is like all or nothing for their future.