I would and I did go for Helheim. It swings 12% faster than Laphria by default, and is not hard to gear to 5-hit, 100% datk. Laphria has appreciably higher base damage for harder hitting autos, but Fimbulvetr has superior SC properties and damage calculation vs. Disaster and its autos come out faster.
If you're finding substantial advantage in damage with Laphria, then you're probably not using an appropriate set for Helheim. It's fallen into this weird group think where people just want the, "signature" weapon of WAR to be the best, so everyone seems to be chanting ad infinitum, "Yeah Laphria is slightly better overall plus BREAKS!" Which, you know, if you need Breaks for content, then you can still do them and weapon swap(or you could be realistic and have your BRD do Shell Crusher cause breaks other than DEF down are usually not cared about, but if they are they are worth the weapon swap). The horror!
That said, Disaster does have the cooler WS animation. Just can't beat a giant sun shaped explosion. Thanks Metatron Torment! (Course I'm still really fond of Scourge, as it looks like opening up heaven with a small halo at the top, and then slicing through the firmament of reality)
But I would definitely go for Helheim, especially if you are interested in the other jobs on it as well.