ZDad: I think it’s more like 1 or 2 percent. And the Modern Orthodox attrition rate is a LOT higher.
Tuna bagels or whatever you call them, as bad an influence as they can sometimes be, have a major advantage that their kids will continue in Frum mosdos and hopefully remain Frum. And very often when these people themselves reach middle age or so, they turn back to practicing Yiddishkeit.
Whereas when someone literally leaves, it’s much harder to come back and they’ve most likely messed up their families.
While it’s not easy being a kid in the former family, and kids can definitely sniff the truth and smell hypocrisy, if they have a solid Torah education with the right hashkafah kids can decide they want to be frummer than the parent. If it’s both parents that disregard some of the Torah, of course the child will usually end up a lot “worse for the wear”.
The bottom line is usually how bad of “tuna bagel” one is, is it insidious in lack of belief, or more of “I can’t be bothered with all this minutiae” so I’ll cut some corners. And where one chooses to live and what kind of Yidden they surround themselves with greatly effects their chances of Teshuva, as well as their children’s success in Yiddishkeit.