I have given the Texas Bowie law some thought. Bowies are very lethal knives. A stab or slash from something like the DFLE would kill you a lot faster than most of the pistols of the time. For all the Colt .45 SAA's there were probably dozens of little derringers and pocket pistols and unreliable cap and ball revolvers.
From what i know the law about bowies in Texas has been around for a LONG time.
Even nowadays with Hicap 9mm's a stab wound is twice as likely to kill as a gun shot and most stabings are with much smaller knives than the bowies.

Maybe you are not supposed to take a knife to a gun fight because it would be cheating?