Yeah I ran the numbers somewhere and Grant's contract put him in the 4th highest on a team, but that doesn't account for rookies. I think it is something like 2 rookies start on average, which bumps him to 6th on a team. Grant got rotation player/spot starter money. That is what he is and his minutes, even in Dallas reflect that.
The real issue he had in Dallas is he wasn't shooting well after the first couple weeks of the season.
How can 2 rookies start on average? That would be 60 rookies starting on 30 teams. I guess you mean on average 2 on rookie contracts are starting? That seems possible but still high.
At any rate, I still think that DAL signed Grant thinking he was going to be a starter and he was a starter, until they realized he wasn't that good. The Celtics didn't see him as a starter so they likely were offering less. I suspect that moving forward, teams will use their NT-MLE (those that have one) on players that are expected to be starters, just like DAL did with Grant.
It is certainly true that teams resigning their own may pay more for a bench player, especially contending teams, but I don't think we are going to see all that much of that. There will be top teams where all the starters make more than Grant, but that will be more the exception than the rule. There will be 2-3 max or super max contracts, there will be a couple in the NT-MLE range or lower, and there will be rookie or min deals to fill out the roster. That is how the CBA is going to force teams to build their rosters.
If teams are paying more than that for their bench players, they just aren't going to be able to remain competitive.