It seems like it becomes a bit of a game to figure out how to phrase a question so that it is not closed. Wouldn't it be much simpler for all concerned to just consolidate both sites, so as to avoid all the fuss about how a precisely a question is worded?
Well for starters the Biblical Hermeneutics site is not a Christian site, even more than this one isn't. Jewish interpretation is part of the purpose of that site.
The two sites used to have more overlapping scopes, but now they're mostly complementary. This site focuses on the documentation of Christian groups, so any exegetical questions must be scoped to a particular denomination or group. (Though we also prefer that questions indicate why they think the passage is of particular relevance to the denomination. Some questions that seem to just arbitrarily pick a denomination may be edited and migrated.) Questions on Biblical Hermeneutics however are not allowed to restrict answers to any particular group.
The two sites also have very different expectations on how answers should be written: on this site answers should provide supporting evidence that shows that the particular denomination/branch does teach what the answer says it teaches. On BH.SE answers can present eccentric readings that have no support by any denomination, or even completely new interpretations, but what they must do is provide evidence that supports their arguments. These two approaches also mean that the two sites also have two different communities - there are people who love explaining their own interpretations of the scriptures, but who would hate this site's restrictions that all interpretations must be conform to the teachings of the denomination the question asks about. Conversely there are people who only want to hear official interpretations and greatly distrust the individual interpretations you'd see on BH.SE.
Questions about who authored a book of the Bible generally belong on BH.SE, though if they did request a denomination's views on authorship then this would be the right site. Your question is a good question and I think its natural home is on BH.SE.
The first question is one that I considered migrating, and it could still be migrated in the future. Part of why I didn't is the rule that you shouldn't migrate low-quality questions, and to be honest, that question is not as good. I think it's a bit confused, probably based on mishearing that Mark's Gospel presented Peter's perspective on events, but the way that it's written sounds like it asks whether Mark wrote Peter's epistles, something I've never heard anyone ever suggest.