You and OP are actually agreeing with "the correct answer is it depends and now let's discuss context". This echoes my experience as interviewer too. It's a red flag when the candidate responds with "the correct answer". That's what OP is calling out.
I'm replying here because I get the impression you're looking for "the right answer" as you see it: "the first step is to mitigate then do root cause". You're right! But it also could be too adversarial.
Most interviewers are adversarial.
Let's be honest - if an interviewer wants you to pass a system design interview, they'll make it work. I see this with particular candidates all the time. If we want the person to make it through - we'll let them get through. If we don't want them to get through - no amount of correct and behaviorally appropriate answers are gonna make them get through.
Also making a queue bigger is a bad reflexive response to queues being full. I was very involved in the SEV review (postmortem) process at Facebook and witnessed lots of cases where bad situations were made much worse by misguided hasty responses.
I agree though, hasty response is the mark of a junior eng
Depends on the function of the queue. If it's a dead-letter queue, there's literally no downside besides a likely-trivial amount of cost. If the problem is upstream of the queue, and the queue is actively feeding well-functioning consumers, yeah, it could make things way worse. This is where being an experienced engineer comes in. Also having 2-person approval like you would for any code changes. Point still stands that you should take low-risk actions to mitigate if they're available to you before root-causing.
This is the opposite of what "people with real experience" do, at least in production-down situations. The first step is to mitigate, the second step is to root cause. If there's some no-brainer step that has a chance of alleviating the issue while you root-cause, and is unlikely to make things worse, you should take it.