Really? I've always thought that katana was very sharp and deadly...
It's sharper, in that it has a higher rockwell hardness (up to 80 versus about 65), but this only makes it deadlier to someone without armor, and scimitars and falchions have similar legends about their own sharpness - shearing weapons 'saw' through their targets, whereas straight- edge double-bladed weapons are much more tactically flexible. As mentioned, the primary weapon of the samurai was the spear and bow - telling when you consider how drastically inferior Japanese armor was compared to its Eurasian contemporaries. Katanas chip easily, and a common quote (I forget who originally said it) is that a sword lasts either four battles or four centuries - whatever comes first.
Katanas are worse off than homogenous blades in that regard - they chip easily, and as with any blade, repairing them means you are removing actual material - but with the Katana, eventually you're going to wear away the entirety of the hard edge at some point, and then it may as well be scrap.
Nonsense. Everyone knows a samurai with a katana would bisect a knight wearing full plate with a simple vertical slash. During WW2, American soldiers targeted the Japanese who were wearing katanas first because their killing power was feared and respected.
There was an island battle where guns were apparently useless. Still wish I knew which one : / Went much like most such battles, regardless.