its not the duo ability itself alone that makes it weaker, there are many things. the atk is lower, the hp in the upgraded is lower, when generated from a nemotoad- the nemotoad is not burrowed and is subject to cc even before the sting ray comes out.
im not too concerned with it being able to be fueled by a
mark, because if a
mark is your only source of
quanta, you will be severely limited in how many applications of future shock you use per turn, as well as likely having to decide between evolving a nemotoad or using future shock on some turns. future shock is generally a rather weak soft control ability, it only lasts one turn, requiring constant reapplication, making its power/cost ratio way low.
also, its worth mentioning that the lack of burrow means this card will always remain exposed to cc and not be able to burrow and reduce the effectiveness of antimatter, both of which i found rather useful in my time using shrieker decks.