It feels like some of this discussion just resolves around the limitations of the rules construct to simulate reality in a way which leads to "credible" outcomes. Eliminating the weapon from the system is simpler than over-complicating the rules to create constraints on the mini-maxers.
Why *are* shortswords popular historically compared to longer swords? Setting aside the risk of breakage (which could be easily modelled with lower weapon HP for longer weapons). I'm no swordsman, but I'm guessing the lower inertia of a smaller weapon in real life is a significant bonus - you can be jabbing a second time before your opponent can bring a very large sword back into position to parry. In the real world, lower levels of armour when shorter swords were popular may have made that an effective choice. In RQ, with easy availability of magical blessings to deflect weapon strikes, there will be fewer reasons to choose a shorter, lighter weapon.
Larger weapons must also be significantly more tiring to use in one hand, even before considering the risk of injury to a wrist or of having the weapon knocked out of hand.
Luckily, the history of RQ offers an easy mechanism to let players use longer swords one-handed without them becoming the only choice: Fatigue Points! Let them use a larger sword (subject to minimum STR), at the cost of a rapid loss of FP. Sure, you may need to extend the RQ3 FP rules to get the right balance of permission / discouragement, but, hey, totally worth it, yes?
It's unavoidable that the game system drives player choice even at the cost of credibility of outcome; but worth noting that in the real-world people frequently make choices that are not rational, and that perhaps this is worth reflecting in the game. People don't choose cult loyalty in the real-world based on a utilitarian evaluation of the magical benefit, otherwise nobody would support Coventry FC. People are stubbornly loyal to failed concepts long after they have been shown to be actively harmful to their own interests. Likewise, it might be worth considering how to encourage players to make choices that are sub-optimal in game terms e.g. sticking loyally with Elmal even while the solar propagandists are promoting Yelmalio's palpably more convincing magic; or choosing a sword that is credible in terms of real use rather than maximised solely in terms of game stats.