Hypothetically, your two example questions might not actually be "too broad", even if they lack an explicit denominational scope.
- Questions about the doctrine of the Trinity often have the same answer for all modern Trinitarian Christians. In particular, I don't think Calvinists have a different conception of the Trinity from other mainstream Protestants, or from Catholics. There are some divisions between Western and Eastern Christianity, and there are differences in theology or emphasis that don't correlate to denominational boundaries. But almost all of our past questions have been pretty generic.
- Anyone asking about sola fide, etc., almost certainly intends to ask from the perspective of sola fide adherents, which would include Luther as a primary and normative example. If they instead want to know about sola fide opponents, that should be obvious from the question. If they want both views, or to know which view is True, then we should politely ask them to pick a viewpoint.
There are many other cases where it's more or less obvious which viewpoint is intended, just from the subject matter. It would be a good idea to edit the question and tags, or ask the questioner to do it, because it's generally helpful to be explicit and it makes tag browsing more useful. We've had some questions where the scope was obvious to some readers but not others, because of the use of insider jargon. In those cases, adding the explicit scope is particularly useful because it stops the question being closed as "unclear what you're asking" by people who don't recognize the terms.
If a question is genuinely "too broad" then it would be best to not answer it at all, unless the scope is subsequently narrowed.