Henderson's window with the Rams is just about closed. He's a FA after this season. He is also a guy who has failed to do his job, which is back up the RB position and carry the ball when the starter goes down, for multiple years in a row now. He gets hurt way too often and wilts when he's asked to run into the teeth of a good defense. And he goes down if someone touches his shoelace.
The only area Henderson is a plus back is in the pass game. That's not enough to hold down a RB2 spot on a championship roster.
Kyren's a guy who can carry the ball for you vs a good defense. He has good power and contact balance. But he's also a solid pass catcher so you don't lose too much there if anything.
I figure it will take maybe half of camp for Kyren to take that job. But worst case for him sometime during his rookie season he'll seize the job.