I think someone explained that the Booker deal when stated as being $153M for 2 years is including the maximum possible salary (which includes a trade kicker). The base salary is 2 years added for about $133M, if my math is right (and based on Spotrac numbers).
For the next 4 years, Booker and Brown will make about the same, about $235M for Booker and about $236M for Brown. Booker will now have one more season at about $69M in 2029-30 but Brown will be a UFA, if not otherwise extended before then.
As to value, this is just what guys like this are going to get paid. There are huge risks for the teams, if these guys get injured or decline, you have a bunch of cap tied up in them. Just the cost of doing business in the NBA.