Composer Giacchino himself was a late addition to the film - he didn't have a lot of time to work on the score and was not given any instruction to deliberately mimic Williams:
"Giacchino only had four and a half weeks to compose the music for the
film, beginning almost immediately after finishing production on
From the same interview:
Kathleen Kennedy says they’re trying to break from some of the
traditional Star Wars tropes, like doing away with the opening crawl.
Sounds like that applies to the music as well?
Kathy said that to me, too — “No one is asking you to do what was done
before.” I feel it’s important to be me, but in this universe, we’re
working within. That was sort of the challenge. It was never sort of,
“Oh, you have to do this, this, and this.” It was always just: “Here
are the emotions that we need to cover.”
Other than the volume and surprise factor, I find little musical similarity between the two sections of score in question. Rogue One's track "He's Here For Us" begins with a very fast note progression from low to high and then has the loud 'hit' or 'stinger' - compared with the "Main Title" of the saga films, which opens with all instruments playing a chord in unison.