Random is Random is Random. It all depends on your luck.
Do you generally have good luck? Then you're probably fine running blm/rdm instead of blm/brd.
Does the game hate you? Every time you don't /brd, it will be /brd at least 50% of the time, purely because the game hates you. You can laugh at this and say the numbers are totally made up, but every one of you has experienced this and knows full well that the game's RNG loves to @#%^ with us. It's almost ALWAYS the proc you DON'T have, or if you have them all, it'll be the worst possible proc choice over and over. I remember one run doing an nm with a pld tank (back when abyssea was still hard, before heroes and when scars was still fresh, I don't remember the nm though), where like, 4 pops in a row, the trigger was flash. We had a bard, a blm, a blu, and a nin. The trigger was still flash.
That said, those of us wars who happen to have our various weapons skilled up don't get to complain about having to set nothing but regain atmas (ie: having to set @#%^ing sea daughter... *twitch*) when red procs are needed lowman, so why should you get to complain about having to sub /brd? Quitcherbitchin. Proc bitch is proc bitch. You're very much NOT there for damage. Anything
can put out absurd damage in abyssea. You're there to proc, because blm is really the only procing job besides bard that can get enough m.acc to semi-reliably land threnodies