It doesn't matter how much you think my attention is "really worth". If I want the service now, have no cash, but can pay with my attention, I am strictly more enabled than if the service only accepts cash.
The fork between (1), (2) is how much cash their attention is actually turned into.
To put it another way: what's the attention of a poor person really worth, in dollars? Answer is always less than or equal to the amount they can spend.
I mean I supposed every transaction leaves someone poorer of something and richer in something else. I'm not sure of the point though.
I concede that if the ad companies are willing to forgo collecting X dollars in exchange for showing you an ad then it must be worth >=X dollars to the ad company for the person to see the ad.
But it remains true that the poor person has no way to convert their attention directly into X dollars, and all that taking away the free tier does is make it so that someone who would have made a trade (of their attention for a service) cannot do so.