As I wrote, "I would be generally loathe to interfere unless I thought input would be welcome." So, I'm not going to defend any position against your hypothetical argument as to whether I would intervene or not. It's entirely dependent on the situation. I would be using my best judgement in said situation. Also, I may be an expert in one type of gun or optic compared to the LGS employee, who has to have a broad knowledge base without the depth in some peculiar area. This is true of humans in general. Someone may speak with authority on a number of subjects, but I have my areas of expertise too.
Right now, you're intervening about hypothetical situations which may or may not warrant intervention. And, I wouldn't call it 'intervention' if the help/advice/feedback/corroboration is welcome, but this requires an ability to "read the room". This includes but is not limited to non-verbal or subtle communication which invites the feedback. Customers do this all the time with each other, and so do LGS employees whom I know and respect. They know I'm not coming for them.
This could work for or against the advice of an employee or customer at a gun store, but I'm not trying to upset anyone at a gun store, let alone my local gun store. I've learned at my old age that not everyone is stable, no matter how 'correct' the advice or correction. This again leads my default to be, "Don't intervene". And, we're talking about people with access to guns here, so an abundance of caution seems pragmatic. If you've ever tried to make a valid but trivial correction for someone on the Internet, then you know of which I speak. What's surprising is not that people make mistakes but that some people go absolutely bat

crazy if you correct them...about anything.
I would only intervene *against* an employee if the advice were flat-out wrong, but anyone who has a modicum of intelligence, courage, and stoicism wouldn't mind a valid correction, especially if it's a mundane detail they wouldn't be expected to know. It's also fallacious to assume that a correction means one thinks the person being corrected is an idiot. I've been corrected a lot about this or that, and I know I'm not an idiot.
If they can't handle the correction, then they probably won't be my LGS for long depending on how they react. In essence, if I wouldn't mind the correction then they shouldn't either. I don't hold someone in high esteem for the perception of 'never being wrong' (especially in 2024 with ready Internet access) so much as having a calm and rational demeanor—and that would mean they could take correction in stride. I have far more respect for knowledge with humility than someone who attempts to play the 'know-it-all', though I'm always happy to learn from those who know more than me.
P.S. I changed my username to match Reddit.
P.P.S. It's always wrong in English to add a space before ending punctuation. Let's see how you handle this correction and feel free to look it up. It might be that you assume of others your own personality traits/quirks. If this correction enrages you then I invite you to think about how you're projecting your attitude on to others.