If I understand correctly, Jon takes issue with 3e's Exigents and the use of Evocations to represent artifact powers, in part because their build-your-own nature puts the onus on an individual player/ST to write a lot of Charms in order to be playable. This can be a tricky process for someone new to Exalted - as you're discovering! - because you're trying to learn the system, learn what is and isn't thematically appropriate, and write material that is not too weak or powerful.
That said, I think what you're encountering right now is less due to the whole concept being flawed (which is not a take I would agree with - and I should clarify, not necessarily what Jon thinks either) and more because the Exigents book isn't out yet. It's a hell of a lot easier to handle artifacts right now - virtually every new book has had some examples, and there's a whole book full of them. That gives you a lot of potential places to start - example gimmicks, Evocations you can compare yours to for assessing power, charms you could just borrow wholesale and reskin / retheme to fit what you're looking for, etc.
The ideal state of affairs for Exigents is that if you're interested in having one play a major role in your campaign, you'd look at the Exigents book, see what they have on offer, and then decide either a) one of the published Exigents works for you (maybe with some tweaks), or b) you feel capable enough to use those examples, along with the guidelines for creating your own, to make something else. Without either of those things, it's a pretty tall order, as you're discovering.
What I would recommend doing if you haven't, since this is an artifact linked to an Exigent, is thinking about it in terms of the god responsible. Really nail down the specifics - more than just the thousand-foot view, as best you can. "A volcano god" gives you a lot less to work with than "the Western god of Volcanoes and Fireworks, who's feuding with the directional god of Sharks." Having some idea of what the personality, purviews, themes, and goals of that god are will go a long way toward what kind of powers an artifact blade tied to them would be able to grant.
It's also perfectly legitimate to say that the sword served as a vessel for the Exigence, but has its own themes. That suggests something vaguely tied to the god in question, but that stretches thematically in a new direction (which is nice in its own right, because that gives your Exigent a way to develop new capabilities if need be). This also frees you up from trying to write Evocations that hook into the Exigent's charms directly.
Finally, since this is a PC's retainer, and isn't meant to outshine the PC themselves, keeping things at the less-detailed level of QC charms is a perfectly sensible move. Unless and until they start taking on a greater role in the plot, it's perfectly fine to give them one or two 'functional' powers that let them perform well or have a little trick in the areas they're supposed to, and one or two 'flavorful' powers that sell people on the concept that they're an Exigent of So-and-So.