Not necessarily true. But it largely depends on what the Jazz decide to do with Exum and Favors.
Locke gets his numbers by assuming a roster of Gobert, Ingles, Rubio, Mitchell, Burks, Bradley, next year's first, Hood at a cap hold of $7M, and minimum roster holds. That totals ~$80M. Jazz would have to renounce rights to Favors, Exum and JJ and decline options for Jerebko, Sefelosha and Udoh to get to that amount. That's really not "waiving everybody." Jazz still have 8 players under that scenario. They'd be offloading mostly end-of-bench talent to add another very good starter. Or maybe they trade Burks and keep a few others. Exum's cap hold is around $15M so can they sign him for less? In that scenario, the choice would be between Exum and Burks (if they could find a trade partner).
So, yes, Jazz could sign a player for around $20M and then give Hood his raise.
I think that's part of the reason. But the main factor is health and inexperience. How do you value Hood? His camp obviously thinks he's worth $20M (or more). The Jazz see a player who can't stay healthy and has never been a #1 or #2 option but wants to be paid as one. I don't blame Utah for saying "prove it." Besides, if Mitchell explodes, maybe Hood isn't even re-signed. Insert Donovan into the starting SG slot and look for a bigger SF via free agency or trade. Or maybe the target is a PF and Utah continues to go with Ingles and other options at SF.