I also would add that there is a lot in between the two categories you mentioned. There are also many members of the non-MO community who don’t care much about yiddishkeit and are going through the motions. But it’s the ones who do care but have heretical hashkofos and sinful behaviors (rhat they try to justify) that are worse. If someone just says “I’m not so religious”, that’s a shame, but it isn’t a threat to Judaism itself.
There definitely are some people who are in the MO world who are just shy of ner yisroel/out of town torah institutions. That’s true in eretz yisroel too, where aside from nationalism, there are bnei Torah who wear kipos serugos who are just as committed (and probably moreso) as i am.
I believe the disinterested people are not nearly as much of a threat as the haskalah influenced ideologues. Rabbis who learn alt but are attempting to undermine torah and perpetuate the sinful standards of the mostly ignorant masses of MO. Rabbis who believe in secular education as an ends to itself, feminism, LGBT rights, bible criticism, evolution, gender theory, and tons of other issues. They might learn day and night, and that’s why they are much more of a threat to Judaism.