You did not get me

The soft sign does not belong to the ending.
You confuse pronunciation and spelling. Pronunciation is primary, spelling is a way to render the pronunciation in writing.

Compare two nouns in their pronunciation (the square brackets mean it is the phonetic transcription):
[с т р у н А] (nom sg, "string") -> [с т р У н]
[б А н' а] (nom sg, "bath") -> [б А н']

Do you see what I mean? The first noun (струна) has its stem with a hard consonant before the ending, the second one - with a soft consonant.

And let's write them with letters:
струна - струн
баня - бань

Actually, both струна and баня have the same ending - it is the feminine ending [а].
But the final consonant of their stems is different.