I don't play many games, but those I've played all seem to have either grind or $ DLC... either stuff you need to get to Level 50 for or pass the game five times on Ultra Nightmare or something. I don't think I've ever seen a game that slips DLC into the regular game. I guess maybe some DLC are levels or whatever you can just jump into, but "Special Vehicle Cargo missions" are just missions you can jump into at any point. You may not like "Special Vehicle Cargo missions" gameplay, but as much as I enjoyed the Arkham games I never enjoying the arena combat DLC. IME there really aren't many if any games where you just get the DLC in-game.
I do agree there should be some "fuck about" mode for new content, though maybe not for the same reason... You can try very little before you buy, and it sucks dropping coin and finding out you hate it. I might actually buy a shark card or two if I was sure I'd enjoy the purchase... I'm sure as shit not trying that hard for anything without trying it first.