You’re right, it was far from perfect before the Reformation- and much has improved since then. More on exactly what has improved in a minute. To your other point- it continues to be clear what being a Christian is, it has been very clear for quite some time. Being a Christian means you belong to one of the monotheistic religions in this world (those being, primarily, Christianity Islam and Judaism) and the particular monotheistic religion that you belong to is the Trinitarian one. Granted, there is such a thing as Marginal Christianity where one restorationist group attempts to expand the definition to include the existence of other gods, albeit without worshiping them- and another may attempt to expand the definition to include people who basically follow the Bible in some way while denying the Trinity. These types of people are not doing anything new, if you aren’t familiar with people denying the Trinity throughout history then you aren’t familiar with history. These two basic points are as clear now as they have ever been- Christians are monotheistic in the sense that one God is worshiped, the only God who has ever existed, and Christians are trinitarian. Again, this is clear now and it has been clear for a very very very long time.
But what of the things that have improved since the Reformation…that would have to do with the issue of coercion. Prior to the Reformation, politics and religion enjoyed too close a relationship, and through the relationship the church and state could work together in all sorts of ways to coerce people to believe certain things and recant others, else be expelled from the country or in some very extreme cases killed. Here’s an exercise for you- name any heretic from the first eight centuries of Christianity. If you just named one, there’s a fairly good chance that you can look up some information on that person, find out where they were born and raised, and find out where it was they were exiled to once their teachings were declared heretical. Actually, if you look at Augustine- he wasn’t even a heretic, but he was exiled on three different occasions that I know of. His rulers were good at being coercive, but they were not good at making up their minds- nor were they particularly good at ruling, at least not to the point where they are regarded as being among the best rulers in the history of the world. Where was I?
Ah, clarity and outcomes. Teaching that is anti-Trinitarian (just one important example) still are what they are, and clearly so. It has been clear for a long time. The biggest difference from pre-Reformation to post-Reformation was that before the Reformation, at least within Christendom, the Church had the backing of the State in the interest of coercing silence from such people. After the Reformation, the Church gradually lost its monopoly on religious coercion, and then it slowly let go of that capability altogether.
When you put it in terms of coercion (as I most certainly insist on doing), your perspective changes a little, doesn’t it? Instead of seeing a Church that clarifies and makes things easy, you see a Church that used to wield a coercive power and thank God it doesn’t wield that power any longer. And that is the main improvement that came from the Reformation. Was it your wife that belonged to some sort of cult? Well, now that we are post-Reformation, all you could really do was try to change her mind. Pre-Reformation, her cult could have been forcibly disbanded, its leader sent elsewhere, and your wife could have chosen to be exiled from the country as a very loyal follower or renounce her previous affiliation as she’s brought back into line by coercive means. Let’s be very clear- prior to the Reformation, that is how it worked. It was brutal, it was harsh, and it was an inappropriate use of power and authority that impinged on religious freedoms that have Always existed for All people, even when they were neither recognized or respected on a pretty consistent basis.
You should not miss that aspect of Catholic history. Enjoy your religious freedom, and while I do understand your concern for your family, do allow them to enjoy their religious freedom as well.