Seems fair. Baker can push Polk for that last spot. Bourne is basically “one of our planned starters gets hurt” insurance. If all goes as expected then I’d say it’s most likely that Polk is the sixth on the roster, Bourne gets traded for a 6th, and Baker & Chism both go to the PS. Perhaps Bourne also makes it in place of Hollins if Hollins’ injury lingers and he starts the year on IR.
I could see some team like Houston claiming Chism, since Ben McDaniels is the WR coach, they like to feature the slot WR too and their guys are banged up or signed elsewhere (such as Diggs), but otherwise he’s probably safe unless he really explodes in preseason action. A lot of teams don’t really use the slot to the degree McDaniels does.