Like, how polished would all 3 acts be if they didn't spend an inordinate amount of time fine tuning Act 1? Having 3 "Decent" acts could be considered better than 1 "Good" act and 2 "Bad" ones (Even more so when Act 3 is typically the climax of the game's story).
(...)
That assumes that all of the team work on all of the content. While there is certinainly some overlap, I suspect the truth is far more complex than that. Every development I did manage to get a peak into (decumentaries, interviews etc.) tended to develop areas simultaneously - breaking bigger team, into smaller teams each developing and having creative control over their own part of the game, with oversight from above to make sure it all fits together.
I am also doubtful because act1 didn't change THAT much throughout EA. so I am confident they worked on subsequent areas throughout most if not all of the EA - there were mentions of amazing verticality of the city of Baldur's Gate very early into EA. There is also the assumption that feedback from EA didn't affect later areas. Probably biggest consumer of reasources was the actual release of EA build every couple months - but that's part of most development processes - publisher, showcase Demo's, playtesting builds - but a public, playable release probably took far more work than something shorter and more contained.
If EA had negative impact, it might have more to do with how the game is revealed, and Larian's commitment to the content before the game is finished. By keeping their cards hidden, they would have more freedom to change/cut things as they wish. Let's be honest here. A lot of complains have less to do with what we got (which isn't free of criticism) and more with what people were promised or imagined they will get after playing act1 over and over again over the years. Perhaps playerbase would be more forgiving if taking whole of the game at the same time, perhaps, Larian would be at liberty to change things more drastically for better continuity.
All we can say for certain is EA and its extended development time is overwhelmingly positive for the specific act being worked on. (Which is not a particularly groundbreaking revelation...
That I flat out disagree. IMO best changes in EA, were related to systems and gameplay and those affect the entire title. If things like disengage on jump, disengage as bonus action, advantage on high ground and backstab, automated reactions, hotbar-only UI and many, many other stuff that I am sure people mostly forgot existed by now were shipped with 1.0 BG3 would be a much, much worse game. It is of course impossible to guess what would and wouldn't make into final build without EA. But IMO thinking that EA affected act only would be naive.
Not to say that EA didn't benefit from two years of aggressive testing, but without it we would just get an untested act1 - not better tested acts 2&3.
There is also a matter of other benefits of EA - a major cash flow, proof of great interest in the title - which would encourage Larian to invest more into BG3 than what they might have planned initially - and possibly get additional funding from third parties to make the game bigger and better.
