An interesting question and one that will have a lot of debate for sure. My take on it is not so much just on Breeze but will Payton be there after Brees goes (maybe this year maybe the year after depending) as i think his offensive mind will actually make the biggest difference.
DJ has a poor QB yes, he also has a poor O Line, poor complimantary weapons (largely due to Rosen/O-line) but he also has a unproven and so far fairly average looking OC and a defensive head coach. Kamara has age on his side, a top O line a true number 1 WR to help, argualbly the best offensive mind in the game calling plays so this makes a massive difference in their value now and the immediate future.
Player type wise if Kamara has the backfield all to himself next year will he hold up to workhorse volume all year that will be of interest. For me though if they win the SB this year and Brees walks away and Payton wants to go for full HOF credentials and gets an offer from GB he cant refuse to work with Rodgers then i would be slightly concerned with Kamara and it would put his value in flux for sure.
As long as Payton is there I would have full confidence in Kamara being a top 10 fantasy RB, maybe the drop off from Brees doesn’t let him crack the top 3-5 but as long as the QB is competent and Payton will ensure they are that at least i would treat him as a top 10 option who can be top 5 if they struck gold at QB after Brees has gone.
DJ though i can see as a high end RB2 but inconsistent week to week based on matchups and unless Arizona and Rosen can really turn it around this offseason and into next season he will likely be that for the remained of his career given his age and situation as it is. Needs to improve for him to be a solid RB1 again.