Given this context, could more brittle but harder swords or other weapons be preferred?
There's a more important question here that you haven't answered, which is "What is the benefit?"
Super-hard materials are useful at cutting and breaking and penetrating hard things, but when fighting against unarmoured opponents who are presumably using no more substantial protection than a wooden or leather shield, what's the benefit of your tungsten carbide gladii? Seems like there's at best a small incremental damage improvement over the use of more conventional metal weaponry, which is easier to make and sharpen, and much tougher.
So I'd lean towards "no".
Also, this probably isn't a safe assumption:
So against unarmored opponents, it stands to reason that swords will only meet cloth, flesh, or wood (shields).
Where metal was available, shields often had reinforcement. Polybius wrote of one design of Roman shield,
Its upper and lower rims are strengthened by an iron edging that protects it from descending blows and from injury when rested on the ground. It also has an iron shield boss (umbo) fixed to it which turns aside the most formidable blows of stones, pikes, and heavy missiles in general.
Obviously, not all shields had this kind of reinforcement, and a society that had little metal would seem likely to prefer things like metal spearheads as an efficient use of limited resources, but as you're talking about opponents with metal swords there's a chance they have reinforced shields too.