The Writer's Guide matters if it's not contradicted onscreen since it's the next best authoritative source because it shows the intent unless it's later contradicted.
Kirk's first command is a destroyer equivalent class ship.
Check as there's reference to Kirk's first command in WNMHGB. The onscreen reference validates the intent of what is in the Writer's Guide bio. That tidbit tells us something important. Kirk has command experience before he commands the Enterprise
. And that makes sense that Starfleet would only give command of a capital ship to someone who is tested and proven. It's credible.
What it comes down to is you want
it to be TOS Spock in the film portrayal. Fair enough. But don't get pissed with us if the evidence mounts that it can't be the TOS Spock. It certainly doesn't invalidate your enjoyment of the film. But it does establish that Abrams and his crew didn't do their homework if they really wanted to maintain a tenuous link to previously established continuity.
Intent matters when it's corroborated with what gets onscreen. TOS (in regards to Kirk) corroborates GR's intent with what is in the Writer's Guide. ST09 fails to corroborate whatever intent Abrams and even Nimoy may have intended because someone didn't do their homework.