What I tend to find is that the B sounds weak by comparison on passives, while on actives the you can get a strong B with EQ, but that leaves it sounding fake and lifeless compared to the higher strings. You also tend to get weird bell-like sounds on the B string, especially on the higher frets.
Incidentally I've never had this problem people talk about with a 'floppy' B... it's just the sound.
I've never played a passive 5er, and haven't experienced what you're talking about with a decent active 5er - although I tend to use a 5er for it's lower notes, and don't usually play one very much at all above the 6th fret for the most part...
Just out of curiosity, what specific 5ers have you played???
- georgestrings