Both philosophies have their merits.
Open worlds feel more realistic, they let you move around at your own pace, do things in basically any order you want. It can let you figure out and solve problems on your own.
Linear design's strength is telling a coherent story. If you have to go from A to B to C in that order, and can't go from F to A to C to B to D, this makes the story flow better, and have a consistent pace and buildup.
I did like the open world of Divine Divinity, but I did not mind the linearity of Divinity 2's cut-off point, because that made the threat of Damian real. He wasn't a nebulous guy just hanging out in a fortress waiting for you to come kill him, he was active and causing problems.
Yes, some people were probably upset at not being able to finish off one or two quests, but it also made the players react emotionally - Damian killed people they knew, people they had helped. That drew the players into the story in a deeper way than if the valley had stayed safe and untouched forever. It gave you a reason to care.
Divine Divinity took place in the middle of a war between the humans and orcs. That war stayed basically static. You could fight as much or as little as you wanted and it changed nothing. People would have understandably been annoyed if the orcs could sweep the humans away and overrun the lands and kill people, making a lot of quests unable to be completed. That's part of the paradox of open worlds, you get freedom to move, but the world must mostly remain static and unchanging.
In Divinity 2, you had plenty of time to do Broken Valley before its destruction. It sent you to the Maxos Temple and Sentinel Island as well, which had higher level enemies. If you'd been putting things off for that long, it was your own choice. Plus, Talana gave a very clear warning before the point of no return. If all that time spent wasn't enough to make you finish up Broken Valley, you had no one to blame but yourself.
