NO! BAD! WE DO NOT SPREAD BULLSHIT MYTHS ABOUT MEDIEVAL SWORDS!
Having a higher carbon content does not mean "IT COULD CUT A MACHINEGUN IN HALF CUT A KATANA IN HALF!". It just means it's harder, more flexible, and could likely hold a sharper edge. That fucker might still shatter on you the first time you take it out in earnest. That's just how steel is, especially weird shitty medieval steel.
Medeival smiths had no idea what steel was or how to make it on purpose. Sometimes a given method or ore or whatever would produce some steel but without any understanding of how chemistry actually worked medieval smiths were firing blind. Any actual steel produced was a happy accident.
Ulfberht is a name engraved on a bunch of swords. Some of them are really nice swords, some of them are just okay, and more than likely there were different people making them over a span of time. There's speculation that the steel ones were made with crucible steel traded up from India. In what is again a happy accident, because no one knew what steel was or how it worked, there was a method of smelting iron in one part of India that consistently produced ok steel. We're not really sure how it worked but one theory is that the iron ore was heated in a closed crucible with a carbon source which resulted in the smelted ore having a high carbon content, eg being steel. But no one knows for sure, the records just aren't there. We can only guess.
And jesus no you could not "shear through a katana". Have you ever handled a Katana? They're very thick at the back of the blade, it'd take a massive amount of force to cut through that, even assuming you had an impliment hard enough. You could probably fuck up the edge of a katana pretty bad, assuming you had one of the good ulfberht swords and assuming it was heat treated properly and assuming a bunch of other things.
AND ANOTHER THING!
The good Ulfberht swords are exceptional precisely because most "Viking" swords were... In deference to the smiths of the era I'm going to say "finnicky". But the truth is that Viking era smiths had little understanding of the actual chemistry underlying their metallurgy so their swords were all over the place. There are stories in the Sagas of guys having to stand on their sword mid-battle to straighten them out because they had bent so badly.
AND ANOTHER ANOTHER THING!
Viking fencing, as near as anyone can reconstruct, focused heavily on using the shield to deflect, parry, and trap the opponents sword. Sword-against-sword blows are a bad thing precisely because it'll fuck up your blade. Best case scenario is that slamming your precious, expensive sword in to someone else's blade is going to leave a nick that you can lie to your grandkids about. Worst case is your goddamn sword explodes in to shards that go all over the place, which sounds over the top until you actually see it happen with a poorly made sword.
Ditto with Katanas - Japanese fencing emphasizes using the sides of the sword to parry, not the blade itself. No one was every going to try to "Shear through" anything. All that could possibly do is screw up your sword, possibly catastrophically.
AND ANOTHER ANOTHER ANOTHER THING!
Viking military tactics and Heian military tactics were quite different! Vikings famously made use of the shield and spear in pitched battles, forming massive shield-walls that would push against each other until one side crumbled or was overrun. Heian era Samurai were still principally archers, exchanging arrows before going in to fight hand to hand.
These are totally different swords, used by totally different warriors in totally different ways with very different objectives.
Slamming them against each other is completely pointless nationalistic dick waggling.
TLDR; You can't chop through a sword with another sword. Metal just doesn't work that way. Best case scenario is you shatter one sword and irreparably fuck up the other one. The only way you could chop through a sword with a sword is if you made basically a meat cleaver out of high quality modern steel and then made another sword of out of soft iron and then hammered them together for a day or two until the iron sword eventually shattered.