Realistically, in lane there are few champions that can answer DoT. Lulu, Orianna, and Viktor are the only mid laners that come to mind right now as having shields to mitigate the damage and they are nowhere near as spammable/low cost as Cassi Q. So sure, DoTs have more counter-play built into them, but realistically not many champions have access to said counterplay unless you count popping a health pot as decent counter-play.
This is where I questioned Stashu's decision to take a dump on one fanbase in order to make the other half happy. He could have >either tried harder to preserve both aspects of Cassiopeia or made a new champion where the machine-gun E FITS the champion. Yeah a new champion requires a lot of resource, but the side who liked Cassiopeia for what she was would question why he wasted all that time and resource on the rework in the first place.
The issue raised here is, do you cater to one side and give the kit that fits the champion, or cater to other side and create a kit that >has no relation to what the champion is supposed to be.
For AP rambo, that should have been given to a champion where such a style actually fits the champion.
Who the hell is to say that one direction fits Cass more than the other? Certainly not you or me. Who is to say that a Twin Fang-centered Cassio is not what she is supposed to be? I can argue that she was originally designed to be a fast, sustained DPS version of Anivia, and her Twin Fang is the 'fast' version of Frostbite and thus she fulfills EXACTLY what she was meant to be. It doesn't matter if she's a snake or a woman or a dog or a cat. The intent was to have a champion with a kit similar to Anivia's (where a majority of the damage comes from a single ability - her E) and that intent is entirely met.
Furthermore, I don't see and never saw Cassio as a poison mage. I saw her as a snake woman that was 'cursed' and now has magic powers. Again, who the hell is to say how that magic manifests itself? If it is in the form of magically conjured large fangs then so be it, she's got magic powers now and it fits because she's half snake.
Ultimately, my point is that arguing for her kit to be pushed in a certain direction over another entirely due to thematics as you have been is just a horrible path to go down because every single argument and counterargument that is thrown at you and by you is going to be entirely opinion-based. Why is going down the route of AOE poison mage a better choice gameplay wise and design-wise than going down the route they have chosen outside of thematics?
Riot doesn't see Cass as a champion that should deal massive AOE poison damage. Why should the people who like her as a Twin Fang spammer - which falls in line with what Riot sees her as - have to switch over to a new champion? Instead of trying to petition for them to change Cass, why not petition for a new champion that has a kit specifically around poisoning/crippling people? If you don't want to because you like Cass then why should the people who like Twin Fang-centered Cass get shafted and given a new champion to satisfy their desires?
To clarify, your argument frustrates me to no end because you're basically saying "Hey you alienated us who liked Cass for her AOE poison but really you should alienate the Twin Fang lovers because they don't know what Cass is really all about." It's an incredibly selfish point of view, imo, and what is worse is that Cassio's playstyle has not changed significantly at all. Seriously, she plays out lane the same as she did before the only difference being that her Q does less damage and her E does more. While I admit I liked to max E pre-rework, realistically I wound up maxing Q just as often as E (actually I usually maxed both not taking W until 13). The playstyle is largely the same, the only difference is that you actually have to interact with the opponent now for literally 1 second to fire off two Twin Fangs.
), but not Cassiopeia.