http://www.asha.org/public/hearing/Degree-of-Hearing-Loss/
These are the degrees of hearing loss according to the American Speech-Language Hearing Association.
"Moderate Hearing Loss" falls between 41db and 55db. With a moderate hearing loss, one will start to have a lot of trouble understanding speech. There are some speech sounds that fall outside the "speech banana" with that level of hearing loss, like the "k", "f", "th".
If a CI gives me 20db across all frequencies, that is certainly leaps better than a moderate hearing loss. My SRT is at 15db. So technically that means I'm getting some sounds at 15db, at least in speech. 20db is fairly normal for adults, but children with normal hearing should hear a little above 20db.
With unaided profound hearing loss, my hearing aids got me up to 45db, in the mid frequencies, which is in the moderate hearing loss category. My CI gives me 20db. Either you have a thing or two to learn about CIs or you are denying their potential outright. No CI audiologist would be satisfied with their patients hearing between 41-55db.