Sure, she's not the hardest. I'd say Ayane, Helena, Akira, are all harder to use. But I don't see many (if any) other characters that are harder to use than her.
Interesting.
Characters harder to use than Lei Fang in my opinion would be:
Akira, Ayane, Bass Armstrong, Lisa Hamilton, Rig, and Brad Wong.
Characters easier to get the basic functional ropes down but harder to truly master than Lei Fang would be:
Kasumi, Sarah, Pai, Ryu Hayabusa
Characters that I consider generally easier than her would be:
Jan Lee, Bayman, Christie, Eliot, Tina Armstrong, Hayate, Hitomi, Helena Douglas, Gen Fu, Mila, Kokoro
Fuck if I know where Alpha goes. Also I don't get Zack at all, but a lot of people do. I didn't place him. Maybe Lisa and Helena belong in the second section...
Obviously everyone's subject to their own opinions. Some characters just resonate better, which is why we gravitate towards them. Also we all have biases, particularly assuming our own mains are super-difficult to master. xD