If 100 000 users will say... that some post is helpful and an author should revive $1, how much this author should receive. $1? Curators during voting cannot know for how many users something can be useful.

100,000 users saying that a post should be paid out $1 is extremely strong consensus. It sounds like $1 is almost certainly to be an appropriate payout in that case. Steemit is not a tipping system where we each pay for the value we receive, it's a governance/budget system where we pay out as a collective. I think you are wrong that the collective cannot come to good decisions here, the collective is extremely good at coming to decisions like this when using a median, the phenomenon is known as "The Wisdom of Crowds".

Or lets say, that 10 users will say, that some post is really helpful and an author should receive $100, how much the author should then get? $100?

It would require that the users have the stake to reach that threshold otherwise. The threshold only applies when the r-shares based payout would reach it otherwise.