You need them to Exceed the burst cap of 1m damage. Which, even with Nidhoggr, you're not going to reach for a loooong time.
Still, not having access to an Exceed weapon will put a big stop to your growth eventually.That depends on content. Heals can be really nice to have in long content such as GO. Being strong enough to not need heals is of course always better, though. But good SRs are very few, and having more options certainly doesn't hurt.Phantom weapons drop from Ragnarok Disaster raids, but that's not really something you'll need to worry about for a long time. The main point is, you need five other weapons of the same type to run that Grid. Like, you need five Guns and a Phantom Gun to run a Gun Grid.I don't think that there is any element in modern Kamihime that is F2P friendly... the game is now getting old, and veterans in the game are extremely strong.