I mean, Katana's aren't total garbage. But they were made with what in Europe we would call "pig steel" (melted down iron sand, because iron ore veins don't exist in Japan). The folding was needed because the iron was so shit, and guess what, folding steel was incredibly common elsewhere in the world, they just didn't need to do it as much because they didn't use garbage steel.
Also, the steel and iron they used was very hard, so it was great at holding super sharp edges. Which was great when you were fighting unarmored peasants or people wearing either just cloth or paper armor, since metal armor was super rare because iron was so hard to come by. But just like if you've ever had western and japanese cooking knives, the western ones may not hold as sharp of an edge for as long, but their "softness" means they aren't as brittle and prone to chips and breaks. Which is why you could never make wider or heavier western sword with Japanese steel because it would break even just against a practice dummy.
They were just fine as swords considering who they were usually used on, but in battle outside of duels they were backup weapons, and mostly spears and bows were used anyway. Katana wank is detestable, but lets not overcorrect too much and make them out to be complete garbage. Though if they were used in Europe in the era of armored knights or even just prior but against far more durable swords and shields they would have had a VERY bad time.