Well, as you said, it depends on who you play with. There are certainly some tunes where a particular motif/line is wanted - though can often deviate from it on the verses which aren't vocal or heads. Played a ton of blues including a couple Saturdays a month for about 10 years at The Saloon in SF where we had great players with lots of room for improvisation. Could use all the jazz chord substitutions, chromaticism, etc and insert a lot of the jazz blues changes (such as Blue Monk, West Coast Blues, etc). I can see how it would really throw some people doing turnarounds like I-bIII-bV-bII or I-bIII-II-bII against I-VI-II-V but it was encouraged in that situation... Had Wendy DeWitt playing keyboards on a lot of those gigs and she's a killer boogie-woogie player and on the straight boogie-woogie stuff, it's absolutely true, the bass would have to lock with what she was doing with her left hand. But she could go way out on other stuff. Wonderful player. We also did a lot of stuff with horn section and those tunes tended to be more interesting in terms of changes, etc than some of the typical harmonica based tunes. Anyway, it's a very big genre with a lot of variation - which I think often gets short shrift as it's so often the default in jams and can be pretty uninspired in that context - or that some people can get super orthodox with their version of it.
Here's an example with that band. Not doing any crazy substitutions and bassline is based off a pattern, yes, but then varied a lot and there's clearly room to do pretty much whatever: