Avira > currently a great number of those who claim to want to follow rebbe yishmoel go off entirely or partially in trying to do so, while almost none of their learning counterparts do.
This is the danger, and it was surely happening across the board 100 years ago. I am not convinced that this is the case now, though.
Judging from your writing about “MO”, you are usually talking about people who were not/not very observant to begin with. I see a lot of observant young professionals who went to MO schools and had observant parents. When I see a parent a child together, they see to be on average equally learned – in some cases, the father is more learned, in some cases, the son. I, of course, do not see those who do not come, but my impression is that those from MO/community schools who come from observant parents stay that way, and those who were sent there to be in a private Jewish school also stay that way, sometimes being more observant than parents. Does not mean there is no downwards pressure – I heard from such parents about pressure to be less tzanua and go to Ivy League instead of more Jewishly appropriate schools, but many seem to withstand the pressure.