Honestly steel falchion is better than lava katana, especially accounting for its relative cheap cost compared to the Katana.
The katana deals a bit more damage, but lacks in speed, so if you're already someone who needs help in combat for a better weapon, sacrificing the 'spammability' of an easy bone sowrd/steel falchion for a tiny bit more damage that you have to time swings on is really not going to help.
You also have to pay 16,000g more for a weapon that's going to be replaced by a galaxy sword as soon as you get a prismatic shard anyway, so I wouldn't bother, and don't personally recommend the katana.