People honestly expect too much from this game.
Who is "people", though? You are not wrong,
some do expect "too much". But some isn't all.
I'm not sure if you lurked before the account was made but even in the recent past there's plenty of voices not just here but in general who tuned down specific expectations due to particular announcements. And some turned very skeptical.
And V, is still in certain ways a predefined person with character traits you can't circumvent. They won't reinvent the wheel with this.
Yes, and no. It depends on how you look at it or what you compare to. The character is more customizable in background than others, like an Adam Jensen or Gordon Freeman. I'd say that perhaps comparing V to Mass Effect's Commander Shepard is a relatively fitting comparison. You have a main narrative and story for the plot and your character has a main narrative you cannot deviate from, but background choices or "the past" can be selected from a set of 'archetypes' that have varying levels of influence on the plot or game in addition to the choices you make regardless of your past.
From all statements so far it can be assumed it will bear deeper or more complex impact than in ME. In simple terms you can likely deviate more and customize more (see more effects based on your background) in Cyberpunk. If you liked ME in that regard, you will likely see big improvements in CP.
But comparing ME / CP is just one example that results in a positive outlook for me. In the end, people individually need to come up with their own subjectively fitting or unfitting comparisons, if they want to compare.
I see no issues with what's advertised / hinted at so far in regards to choices or deviating a bit. We get three distinctive backgrounds that will likely influence the plot and give custom content beyond a superficial level.
I do not expect totally different plots per background. You are correct that you'll eventually be set or sent back on track in the main narrative, but does anyone here realistically expect unique plots per background?
Perhaps, TL;DR: Not nitpicking on your preferences, just saying not everyone is "blind with hype" or expecting too much, nor is it necessarily bad they won't or can't offer wildly different main plots per character background but stick to a main one all are part of.
They may not reinvent the wheel anew but at the same time it's not bad in my eyes. I do expect more deviation and uniqueness and, ultimately, freedoms for the player than in other games where protagonists are (even more) defined or characterized, with no choice for the player at all to change aspects of the character, not just including looks.