@Meddler: You reverted Kog'Maw's rework. Please do the same and revert Taliyah to pre-6.14.
She doesn't need buffs or changes. She needs a complete revert.
When you and devs first created Taliyah, you made her an extremely specialist, high-skill, zone-pressure/control mage with a completely unique but amazing and perfectly fine new casting method on her W.
Some people loved her and immediately began to main and practice her and learned how to actually play her despite her difficulty and clunkiness to the inexperienced. Experience made it completely obvious that her W casting method wasn't clunky, it was just different.
In addition, the W lockout specifically PREVENTED her from being a quick burst mage because of the delays on both E and W as well as their animations as an alert. So to land a potentially massively damaging combo, the Taliyah player had to learn how to play her and get very good at her. The E HAD to go first, meaning that was an immediate warning W was probably coming. After that, W lockout means she couldn't do anything else AND had to predict where the enemy would be AND account for them trying to move out of the way. If the Taliyah player was good enough to do that, they were rewarded with a decent amount of burst, but nothing too much for the skill required.
However, those who barely played her because they were lazy or unmotivated complained and whined that her W casting was clunky and the lockout was clunky and stupid and such. Those who had a TON of experience on her, or even just enough to START getting the GIST of her, knew it was perfectly fine and SAID SO REPEATEDLY.
But Riot listened to the former group.
They changed W casting to vector casting. Taliyah's W timing is EXTREMELY important to her. Vector casting INHERENTLY FORCES a human delay, as it will not start until one drags AND lets go of the mouse. Old W casting started immediately on first click. New W FORCES the delay from the dragging and letting go of the mouse. Even those few fractions of a second are a massive delay for such a timing critical ability. In addition, it made it impossible to do a straight vertical knockup. Also, it made it impossible to be free to choose. Old W didn't "choose" a direction until the second click. You had until the very last fraction of a second until it would actually trigger (1s countdown) to pick or not pick. New W FORCES you to pick at the start.
They removed W lockout. This made Taliyah become ALSO a burst mage, reducing her specialist nature and making her generalist. This allowed her difficult E-W combo to be done as W-E, which is far easier and far harder to react to. As a result, her perfectly balanced E damage had to be nerfed into complete and utter trash.
At the same time around then, Q got bonus damage to minions for no good reason. This let her waveclear even faster and in turn, let her splitpush far faster with less punishment. This again reduced her specialist nature even more and made her ENTIRELY generalist at this point. So again, she had to be nerfed into trash in each individual aspect to make up for it.
So now we come to her PBE buffs. What even is this? Are you joking? The increase in damage reduction from subsequent hits PUNISHES GOOD TALIYAH PLAYERS FOR LANDING SHOTS. She gets a buff to early that's meaningless because she was a mage, and all mages are meant to scale into late. And this EFFECTIVELY PUNISHES HER FOR BUYING AP DUE TO THE DAMAGE REDUCTION.
Seriously? Why, Riot? Why can you not just admit you were wrong and revert her to pre-6.14 which would fix every single problem with her? Not every single champion needs to be super generalist and do everything but be shit at every individual thing. And it's not even like what you described in your own post with specialist being too binary. She was still balanced in damage output and zone pressure prior to 6.14, but had utility in her ultimate and W knock which would keep her relevant.
So why?