You can spend hours in the Feywild and not pick up any Soul Vessel even when specifically looking for it.
Firstly, it's a good idea that you can farm any chest for Soul Vessels including explorer chests. It's a reason to run the explorer and open optionals chests.
However, you can do a whole saga on EE or Reaper and not see one. Which begs the question, why isn't the Soul Vessel on the saga reward list?
Or why not give a use for the Legendary Chunk of Ferrocrystal beyond common weapons? Turn in say 50 to 100 for 1 Soul Vessel - not something you specifically farm for, but eventually you get enough just from opening chests.
The current implementation goes against the whole "we want to reduce the grind" mentality you keep saying, to the point where it's probably easier getting the raid items rather than the Soul Vessels simply due to the fact that you can eventually buy your raid items (3750 runes for a set obviously isn't a grind either).