I think with BG3 it worked quiet well as well. It let the devs get feedback on the game mechanics, but limited the story so that the full release still offers something new. It was a good demo, that let people see the direction of the game. And it also let people get familiar with the game engine so modding tools and some release compatible mods where available very early after the release, that allowed to customize the game experience somewhat.

I have not read anyone serious stating that the game was dead, while it was in early access, but maybe because that is a bigger title.