Well you're mostly right in your original post, game was a solid 7/10 on release, but the studio just did so much disservice to themselves by hyping it up for nearly a decade before release, and especially hyping a bunch of stuff that never made it into the final product, and on top of all that breaking their own promise to not release until it's finished.

The whole reason people liked The Witcher 3 was people were convinced the multiple delays to release "made it a better game." It was at that moment that CDPR built the image that they won't release a game "until it's done." They now had their own studio history working against them when they made the promise of "It's finished when it's finished" and people were expecting that. People loved that CDPR was so dedicated to the gamers that they wouldn't let pesky things like money-men push a game out too early when it's half-baked. Oops, they did exactly that with their next game, which absolutely shot all that goodwill from the players right through the heart, especially after already waiting nearly a decade for it.

In the end, are the expectations really unreasonable if the studio themselves were the people who built the hype those expectations were based on?