I thought so too up until the moment she tried to rob Souko of her earnings. After that, well she has to prove that she's any different from Todoroki.
It's because Sumire is a gambling addict.
Sumire is a good person at heart, but she's in a bad place. She failed and gave up on life, dived head-first into her vices (alcohol and gambling). Living life like that for some 5~10 years changes a person a lot.
Todoroki... Well, you see how she is, she's selfish, belittles others, takes advantage of people, sees gullible people as targets, refuses to see how her methods are wrong and instead blames her shortcomings on others...
They are both bad, but Todoroki is miles worse.