Ideally we'd like to have only one question across the sites. Should we advise OP to delete the question on other site or migrate and merge it here?
Cross posting of questions between sites is discouraged since it creates noise and spreads answers across the different sites. If the question were on topic on PMSE, you could leave a comment asking the asker to delete the other question. You could also flag it on the other site for removal.
I went ahead and flagged it on Stack Overflow for removal. Thanks for pointing this out.
I feel like this question is -- at the very least -- off topic for PMSE as it doesn't appear to be about project management. Also, the "design A" and "design B" abstractions make it hard to definitively answer this question since we have no context to decide which coworker the asker describes is right or wrong, and I don't see it helping future visitors. Based on this lack of detail and the nature of the topic, we could close this question as not constructive, not a real question, or off-topic.
Since our site scope is in a state of change, I must ask, what do you think about this question?
This question is helpful in defining what is on-topic.
Should we accept questions about project managers or questions which solicit the opinions of project managers (so the team member who works with a pm gets a better perspective)?
In that light, I'd say it is off-topic since it is subjective/soliciting opinions rather than looking for a "practical, answerable questions."
btw, this seems to be what the asker of How to Adapt to a New Team Culture? was going for and why they came to the site looking for an answer. With that in mind, it would be off-topic for the same reason.
Close or Delete, Don't Migrate
In this specific instance, I believe the correct solution is to either close or delete it. We shouldn't migrate poor-quality or off-topic questions, and I can't think of any site other than Programmers where this would be even vaguely on-topic. Even if it's on-topic, I think it's either too localized or too subjective to be appropriate for migration.
Why Close Seems Better
Personally, I'd probably close it, since it has a highly-upvoted answer that would be lost if it were deleted. I think that's definitely a judgment call, though.