Low elo players dont like 
because they find her difficult...all this time since Taliyah release people saying that she needs buffs....and that she is weak.
I believe that she is weak to....maybe i am a little bit noob to play this champion....or maybe she is bad...
What do you guys think?
She's bad and hard to play. Which is why she's sitting at ~36% win rate in plat+ with people having 100+ games on her. She'll need significant buffs to be taken seriously.
Her W just feels so clunky with quick cast on ;n;
She need some buffs probably, but not significant. Control mage like her take alot of practice due to how they are play and I don't mean the mechanics, so people are probably still adjusting, that's one.
Secondly, she is a control mage that have a cross map alteration, and a range "insec"-like or push away CC. Both are amazing ultility tools that is unheard of before Tahliyah. AND THEY ARE BOTH ON THE SAME CHAMPON, these basically means it will emplify any buff (proabably damage) on a champion mainly there to provide ultility. So I am pretty sure Riot would rather to have her damage be too low than too high during this peroid of balancing. No one would wants another "pls rito, new release champion too opop welp".
Also, historically when control mage like Tahliyah get out of line in terms of being too strong even a bit, it usually is too much. A good example would be how Orianna was in S2. So Riot is probably watching more carefully than normal.
People call her bad because she doesn't really have hard carry potential. She is good as a champion because she does what she is meant to do well. Unfortunately, most people who play this game want to play a champion who gets the most kills, which is why tanks and supports are often the least valued roles. She has actually been favored as a support by many people for this reason. She doesn't really have high kill potential, but she works well with someone else because of her crowd control. She isn't really a support however, she is just a medium damage control mage.
