OK, I know this isn’t accurate, it’s only an illustration, so go easy on me........
Remember the Beatles? You know, John Paul George &
Pete? I guess at some point during their recording career this dude named Ringo (???) was hired by George Martin to come in after hours and redo all of Pete Best’s drum parts since Pete couldn’t keep very good time. Nobody ever told the band about it because George Martin didn’t want to hurt anybody’s fEEElings. To this day we see Pete Best getting credit for all the drumming on Beatle’s LPs when all along it was really some obscure session drummer named Ringo. Right? I know, it’s hard to believe, but it’s a little-known historical fact....
Does anybody see where I am going with this?
1. If you replaced the bass part with your own playing, then it is silly and even downright absurd to give credit to some guy who didn’t even really appear on the album.
2. Don't pussyfoot around the poor sucky bass player pretending he is great, hopelessly feeding his delusions of grandeur. Politely tell him to clean up his act, or tell him to git!
3. If the band is happy with their own bass player’s playing then let them have it. If not, advise them that it would be expedient to begin looking for a more professional bass player. The Beatles were not playing games, and you shouldn't either. They were honest with themselves about their weakest link and made executive decisions to fix their problem. Sounds like your band might not be all that serious yet anyway, so I wouldn't worry too much about pressuring them like that unless they are truly serious (and not delusional about their talent). Point is, honesty is the best policy. Are they talented or delusional? Is it worth your energy to worry about it?
I wouldn't worry too much about a bad bass line ruining your career. The band you are working with is not the Beatles. They are probably not even Starland Vocal Band
. I doubt that very many people will even hear their album. Part of your job is to be a cheerleader and do everything you can to help and encourage the band succeed, keeping in mind that cheaters never win (well maybe sometimes they do win, damn, I wish it wasn't so easy to cheat! Stoopid protools)!
Ethical? No it is not, but I'll bet if you posted before and after sound clips so we can see how truly terrible the original bass line was, some of us might wind up changing our minds!