Well, let me raise a somewhat related question. Consider a person who was baptised Catholic as a child, but they are now effectively inactive in the Catholic religion - they never go to Mass, they never pray, they make no effort to live their personal life according to the Church’s teaching, etc. Now let’s suppose that person meets (for example) a Muslim evangelist, who convinces them to convert to Islam. And as a Muslim, they are now praying five times a day, going to mosque every week, trying their hardest to order their life by Islamic morality, etc. So, how should a Catholic judge this scenario? On the one hand, they have swapped the most true religion for a less true one; on the other hand, they’ve gone from not worshipping God to worshipping him regularly, from ignoring religious questions to paying careful attention to them, from not making any effort to live their life according to God’s commands to trying to live their life according to (what they believe to be) God’s commands (even if some of their beliefs about what God has commanded are mistaken).