These are certainly necessary corrections. But I think correctness is the cart, not the horse.

Writers who make more than one or two errors like these in a 100-page script are probably (there will be a few exceptions) not telling an enthralling story, and it's unlikely they have developed an individual voice suitable to the story / theme.

Correctness is fairly absolute. Some people--not me--would object to your use of adverbs, for example, but "it's" is absolutely different from "its." Only one is correct in a given spot.

Storytelling is relational. Writers have to connect their subjectivity with the subjectivity of the reader (viewer). There are no rules for connectivity, although there are some useful guidelines. You don't know if your script is enthralling until someone has read it and been enthralled.

The problem with focusing on correctness before establishing connectivity is that emerging writers tend to believe that if their script has no errors, it's viable, ready to send out. 99 times out of 100, it isn't.

Sure, if an emerging writer's script is marginally good, a bunch of errors like the ones you describe could sink it with a studio reader who was concerned with such things.

But a truly engaging story, told with a distinctive voice, is likely to make it out of the slush pile even if it has a few homonym misspellings.

An error-free script that tells a story no one would want to see as a film doesn't have a chance.

Proofreading is necessary, but few emerging writers can create a script that is worth polishing. They can if they learn the craft, but that takes time to master, and (more importantly) a love of storytelling.