My position is a bit more nuanced. I think 5-8 hours seems realistic for adding single player to Battlefront and I agree it’s in line with similar titles. The problem I have is that the single player campaigns in those games are always lacking (in my opinion, I know you stated that you disagree).
Battlefront compromised because of the enormous complaining from the first one about single player. The problem is that people didn’t actually want Battlefront cycles spent on making a single player game. They wanted a complete Star Wars single player experience.
I would much rather see Battlefront be positioned as the best multiplayer Star Wars experience that can be delivered. Then align the single player objectives with a different title that aims to be the best single player Star Wars experience that can be delivered.
Neither of those two outcomes are likely true when you are trying to do both.
This is evidenced by the Battlefield and Call of Duty, etc single player experiences as well as the multiplayer experiences of games like Mass Effect, The Last of Us, etc.
While in all of these cases you can argue that they are good experiences, I don’t think you can call them great.