If you had left it at know you want to reject a PR within a few seconds, that'd be fine.
Although with safety critical systems I'd probably want each contributor to have some experience in the field too.
1. What’s the goal of this PR and how does it further our project’s goals?
2. Is this vaguely the correct implementation?
Evaluating those two takes a few seconds. Beyond that, yes it takes a while to review and merge even a few line diff.
You look at the PR and you know just by looking at it for a few seconds if it looks off or not.
Looks off -> "Want to close"
Write a polite response and close the issue.
Doesn't look off -> "Want to merge"
If we want to merge it, then of course you look at it more closely. Or label it and move on with the triage.