I saw fuel costs being balanced multiple times now, but they are still out of balance a lot.
The big solon sink is crafting of armaments, adding solon cost to the very expensive mastershard which get's barely crafted because he is so expensive has an almost insignifcant impact.
With the latest patch, new weapon system got introduced, which could lead to people wanting more different weapons than before, but for sure not all of them since they are going to be super expensive. Not expensive because of the solon cost, but because of crypton cost to farm the materials. Lets just take a look at the Tidal Flail for example.
The amount of runs to farm all those celestium alone let crypton cost exceed solon cost by at least 10x take another good 10x for the rest of the materials. So one ends up by 20x crypton and 1x solon cost for basically the only solon sink we have in. (And thats super low cost estimation for the material, they are likely higher)
Same thing for the other way smaller solon sink, the fusion of Illuvials.
A t5s3 fusion has solon cost lower than 2 s3 runs in OW. The amount of hyperion and crypton one has to spend to do such a fusion is hard to calculate without access to data, but it crypton+Hyperion cost exceed the solon cost probably by the same amount as in the crafting example above.
My buying behaviour in the fuel exchange mirrors what my ballpark estimations about the fuel sinks shows.
And with us getting closer to open beta and me seing fuel balancing still totally out of whack makes me afraid of the balance of the different fuel prices.