The idea that today’s non-frum are tinok shenishba and not mumar lhachis is very far from being universally accepted. It is widely held that they’re not tinok shenishbas if they are exposed to Orthodox/Torah Judaism with even as little as knowing about Orthodox Jews. Rav Berkowitz might hold they’re tinoks but nothing from the Chofetz Chaim supports that notion of tinok shenishba. And HaGaon HaRav Zilber zt’l explicitly paskens as I stated.
The reality is that very most non-frum are not tinok shenishbas. And certainly someone who was frum and R”L became non-frum is considered to be far worse.