DLCs are just skins for armour and guns. They are considered optional ways to 'donate'/support further development, and the devs thank you by giving you a few custom items, and making your name gold in chat so other players know you're a supporter. That's it.
Not only is there is no gameplay locked to DLCs, by far almost all the cosmetics are completely free, and always in-game. Battlepasses are free, and unearned cosmetics go into the loot pool for free. Hundreds of cosmetics to craft for free, hundreds upon hundreds that drop from mission chests.