Yes the problem with severe hearing loss is that hearing aids simply cannot compensate for what is no longer there.
Hearing aids are actually a a lot more complicated than just boosting frequencies. At the very simplest, these days they are wide/multi band compressors that try to balance discomfort with natural hearing, generally focusing on speech intelligibility since that is by far the most important target.
If you have severe hearing loss I would strongly recommend putting yourself in the care of a professional. Costco is a great source of probably the lowest cost versus highest quality hearing aids these days... but the reason I say "professional" is because there are so many kinds of hearing loss and they all affect your perception markedly differently.
It's a lot more than just "missing some sensitivity at some frequencies".