One of the reasons why I'm cautious about CI for deaf babies is simple. It can be very difficult to tell how well a baby hears with HAs....There are right off the bat cases...and there's NOTHING wrong with implanting those kids....but again, whatever happened to all those functionally HOH kids with deaf losses who attended oral schools/programs? See what I mean? Are we assuming that CI is ALWAYS best for severe and profound losses? I do think it needs to be a choice whenever possible......it's very hard to get feedback from a baby regarding how well s/he hears after all......
To address your first point, it is very easy to objectively measure the brain's response to sound using an ABR. If a kid shows no response to 120 dB of sound what makes you think that 130db of sound will be the magical token to understanding spoken language?
Studies have shown that by the time a person has sever to profound hearing loss the outer hair cells are non-existent and the inner hair cells are very damaged. Hearing aids only make sound louder. This works wonders for people with conductive hearing loss since the cochlea is intact. It also works well for people with mild-severe hearing loss because the inner hair cells are present and functional enough to transmit signals.
Once hearing loss gets beyond 85-90db in the low frequencies, it is a good bet that inner hair cells are basically non-functional.
Presenting amplified sound is not only not helpful, it can be detrimental and painful.
I'm not going to say that a cochlear implant is always best for severe to profound hearing loss, and I'm damn sure not going to say it is always best for infants.
I will say that a person with a "full toolbox" approach to education will appreciate that access to good quality sound can do nothing but benefit a child.
Babies who are treated at pediatric audiology centers (especially those associated with teaching hospitals) have basically perfect testing and follow up (so basically kids who live near CHOP and a few other hospitals).
The problem with the "wait and see if they respond" approach is that no consensus exists on how long to wait. Should the infant be fit with super power hearing aids at 3 months, get new earmolds every month for 2 years before somebody finally says that the kid is obviously not hearing anything useful?
By then you have deprived the kid of about half of the critical language learning window. Parents who think their kiddo "might" benefit from hearing aids aren't the type to push a total communication approach and thus the kid loses 2+ years on a technology that isn't meant for profound hearing loss at all.
Is it any wonder that children with profound hearing loss who are not exposed to sign/forced to try hearing aids until they are 2, 3, or 4, struggle to catch up?
I'm not saying sign language shouldn't be involved in children's education. If it is good enough for yuppie babies, it should be good enough for babies who could actually benefit from sign. But sign does not fill the toolbox. Hearing aids don't either. For children with profound hearing loss who show no response to a 3 month hearing aid trial (which is just hilarious for families because the babies have these weird things on and in their ears but nothing changes except mommy and daddy get angry when they try to eat the weird things), a cochlear implant or two is not only indicated by scientific literature, it provides better outcomes when compared to forcing useless hearing aids on a kid for a few years.