Guardians of the Galaxy was released 10 months before Jurassic World. Before that he was best known for Parks and Rec. He absolutely was not cast as a huge star. He was definitely miscast though, and leaning hard on his typical character style in Fallen Kingdom isn't something I'm a huge fan of.As I'm listening to the score, I'm reflecting on the past movies and I think I realize what's "wrong" with the new films (disclaimer: I enjoyed JW and have yet to see FK).
The first movie didn't have super celebrity actors that kids knew and HAD to go see it because of their presence. JW had friggin' Star Lord and even gave him a hero pan shot for his introduction. I just think it changes the viewer's perception and it seems more self aware compared to kids going to see it for the dinosaurs. The very first sequel was even guilty of this with Malcolm's return and treatment.
I don't know if my ramblings make sense or if anyone agrees, but I'm digging the OST as I write this.
World's casting in general wasn't terribly far off from the first one though, to be honest. Brolin would have been a great fit for the series and much better casting.