Yes, there is truth to what you’vebeen told. Unlike a sensorineural loss (inner ear/nerve damage), middle ear dysfunction doesn’t compromise the quality/integrity of the signal as it travels to the brain. The inner ear is what converts the signal into electrical impulses to be sent to the brain, so damage in this area inherently compromises the signal. The main function of the middle ear, however, is to amplify the signal via mechanical processes. In the presence of middle ear dysfunction, the role of a hearing aid is to provide enough amplification to overcome the dysfunction and ensure the signal arrives at inner ear with sufficient volume. So, for example, if someone has a moderate loss that is entirely caused by middle ear dysfunction, we often see that they do very well with even the most basic hearing aids.
With that being said, everything @Neville said is also true. If the total sum of amplification required is such that you are likely to run into feedback issues/restrictiond, or near the maximum output provided by your hearing aid, these factors can limit the benefit obtained by hearing aids. I hope that makes sense. Sorry for the late reply