Cassiopea dps isn't much higher than Victor for a hyper carry. Tested in practice tool...
I did a test in the practice tool because I felt Cass lost her late game carry with her rework. Pls keep an open mind.
Below are the builds
fully upgraded

with

The idea was 45% cdr and to spam all damage abilities.
dps against the target dummy averaged about 900 dps while
did about 1000 dps.
The point I want to make is that Cass has to work hard to land her Q/W in order to do any damage and the result isn't that great compared to
. It's like she lost her late game carry potential with the rework.
Now, alternatively, Cass did get a massive damage spike of 1200 dps with the following build if she added
.
with

The problem with that build is its not really practical. It can be done tho as her AA do go off during E rotations but the target would pretty much have to stay still.
Now, keep an open mind pls.
I would like to suggest Cass E works like new urgot W in that it applies a reduced on hit effect to poisoned targets. You would also have to make it that her auto attacks don't apply on hits, only her E.
The way it would work is that the amount of on hit damage she would normally do with her AA per second would transfer to her E per second. Remember, her auto attack would no longer apply on hit effect.
That way, she can build
to increase dps while remaining squishy bring back her late game carry. She would also give up the utility of
for this.