Someplace in my stash of vinyl I have a Chet Atkins record from the 60's where he played what he called the 'OctoBass' guitar - a regular electric with bass-tuned E and A.
Michael Hedges did a bunch of recordings with a Harp Guitar, which had an outboard set of (IIRC) 4 bass strings. "Because It's There" comes to mind.
Now there were both primarily solo artists, but you're right - these are not new concepts...
And let's not forget The President of the United States of America, with their guitbass and bassitars.
The thing is, so many bass guitar players think that 'bass' mean 'bass guitar' or (for some little more open minded types) 'double bass'.
Bass is not an instrument, it's a register, a frequency range of notes. Just because the tune doesn't feature a traditional bass instrument, it doesn't make it any less valid that tunes that do.
If you're the type of person that has no respect for other styles, genres and experimental music that do not feature a bass guitar in their lineup, then you forfeit the right to call yourself a musician and music lover.