He is making more than James Harden, who is above him in the best point guards.
But I think the Spurs are making a big move here. Maybe they will use their new duo as the face of their franchise. Wemby + Fox and their good role players added in the first five + their good bench players. They are ready to be back in the playoffs. They just need Wemby to be healthy again and create chemistry with the team. Most of them are veterans, so I am sure he is going to learn a lot from them.
First ones to get the contract, will end up getting a bigger one. So let's check the list, seems like nearly none of the names above him, got paid recently, and plenty of people below him too. If all those names had a contract to do this season, then Fox would have still gotten 55 a year, and yet will be outside of top 20. Meaning, give it some time and we will see how they will improve to be a lot better.
This isn't some Mozgov offer, it's normal, it's just that salaries are rising huge now, and that's why we are seeing this. Look at Doncic, dude is getting paid 83 million, nobody got paid that before, so as you can see ,we are reaching a peak where everyone will start to get paid a ton of money very soon from their contracts.
Indeed, if he proves his worth then expect that Spurs will bring more decent offer for him, for now let him and Wemby create a good duo to bring Spurs back to the playoff competitor and who knows if they catch up much earlier we might see them move forward to the finals, there are improvements just like you say as teams always wanted to keep their stars and give that huge offer to let them stay, as long as they are gaining from the marketing and the business still moving forward we will see more and more huge offers from each franchise to have their stars continue to wear their jerseys.