Well?
A fair price is a strange concept when it comes to business transactions. I would argue that the original stated prices for the venue were actually similar in many respects to the E&I tour in 2018. I guess you could say that might be "Fair". I'm not sure how many tickets were reserved for platinum/dynamic pricing. It might have been 25% of the capacity each night.
Music artist are in the music business, and they price their tickets based on their value in the market. Just like when you sell your home, you sell it for market value. I think its rare that you will hear a homeowner claim they sold their house for a "fair price", unless their definition of "fair" is the market value of the home.
The price for General admission tickets, usually the lowest or almost the lowest in the venue, with fans in closest proximity to the band, was a gift U2 had given fans every tour from 2001 onwards. They went from a list price of $45 dollars on Elevation in 2001 up to a list price of $80 dollars on the E&I tour in 2018. With the Sphere, those low prices are gone with $270 dollar priced tickets and this is indeed where fans are getting kicked in the teeth compared to other tours where general admission was a low price gift for the best seat in the house.
So its complex. They have cancelled the gift that General Admission used to be which is sad, but as for the other tickets, their seeing what the market will allow, which is really what they have done on every tour in their history.