I had to look it up because I didn't remember hearing that about the GotG team -- because I was like didn't James Gunn write that? Lol
So Nicole Perlman is the only one who is from GotG and wrote the initial drafts before Gunn came on the project. It's a positive sign, but she's also 1 of 3 who contributed the story for this, and she's not credited on the screenplay (which goes to 4 other people)
From the credits, I get the sense there are too many cooks in the kitchen for this movie, or it went through a few re-writes.
As for solos I would put the entirety of the Dark Knight Trilogy above any MCU solo film, but that's just me -- I think those movies are so inspirational and deep. Scores mean a lot to me and that is one thing the MCU kind of lacks, but it's the teamwork of the MCU that makes me invested in it, how characters crossover and interact so seamlessly that is so enticing.