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.
As for Act development in 1 month...you've made it all because everything or at least major assets, etc was already available to you & quality of everything in BG3 Act is on completely different level in comparrison to such mods as yours and I'm not trying to offend you, it's just an obvious fact.
To create an Act, obviously, they've done tons of preparations but still they need some concept arts, maybe even tons of them in order to create 3d assets and not just architecture ones, quests, tons of scripts, tons of writing\voice overs, some animations for a special cutscenes, visual stuff for atmospehere\immersion, like shaders etc, polishing + remaking\rewriting some stuff they are not fond of which will require some additional reworks for other Acts and many, many other stuff\workflows.
You just can't compare it to your moding experience, you can't say that Larian is lazy and all of this is easypeasylemonsqueezy and can be done in 1 month, it's just pure ignorance and boasting.