I wonder how well securing luggage with a firearm actually helps though.
They did not change the rule regarding putting the "steal me" firearm tag on the inside of the luggage without reason and the same penalties applied back then. I assume the smart thieves broke the luggage open after seeing the tag, stole the firearm, and put the luggage back. Certainly that happens with high value personal items now, so why would this be different from firearms except for the penalties? This would apply to handguns but not long guns though.
Offhand I do not know of any incidents where packing a firearm for extra security created a more thorough response when the luggage was reported stolen but my sample size is low. I would still do it if possible.