This was pointed out in an ascension game I am playing in and I was wondering if their has been anything mentioned in the past.

Prenatural Speed (The Death Cultist Triat) allows a character to make swift attacks or lightning attacks as a half action or on the charge

Storm of Blows, the ascended talent that lest ypu make multiple attacks as a full action with extra added killy fun, replaces both swift attack and lightning attack if a character buys all the required talents to upgrade to Storm of Blows of if they straight out buys storm of blows with xp then they never get swift attack or lightning attack (very rare in an assasin but possible)

By the rules as written a death cultist can not make use of prenatural speed if they take storm of blows as they no longer have swift attack or lightning attack

Is this correct?

Its technically an interpretation that you could hold to be right to the very finest definition of the letter of the rules but I think you already know what the intention was in the rules so that the death cult assasin could be an interesting mobile melee monster.

The "storm of blows" replaces some other talents but you don't have to use them all at once. You can make just 2 attacks (replaced swift attack) or all 3 attacks ( replaced lightning attack) or you can make dual strike ( replaced dual srike and two weapon wielder) or 2 dual strikes ( replaced dual strike and two weapon wielder). Taking storm of blows doesn't mean that you can't make f.e swift attack. In a description of paragon talents stays: "Paragon talent combine the effects of a number of ordinary talents and usually grant a further benefits in addition. The pargon talent counts as all of the original talents for the purposes of prerequisites for other talents , traits or rules." For me if you make 2 attacks it is like using swift attack but still counts as a part of "storm of blows" talent with all its benefits. So I would allow make charge and lightning attack both as a half action if you have "storm of blows" and "preternatural speed"

If somehow assassin didn't buy swift and lightning attack before and now bought "storm of blows" for 500 exp it looks like it counts as he has this replaced talents. If he got ascended with only 1 attack and bought "storm of blows" now he can make 2 and 3 attacks or 4 (if he has 2 weapons) or dual strikes. So it looks like he can use now all the talents that "storm of blows" replaces.

Besides paragon talents you can buy as an elite advance so not only death cult assassin can have "storm of blows". But with the "preternatural speed" trait assassin should be better with "storm of blows" than any other character.