Dota has 100 characters and doesn't suffer from it.

Even if they still wanted to make her a thin, pretty woman, they could have added a tail, horns, wings, floating spirits, flags, or a mount. Whatever fancy thing they wanted to make them both unique.

The more characters you add to a game, the more difficult it is to make each of them distinctive. In a FPS with each character having a unique set of abilities, being able to identify them at a glance is a huge factor to gameplay. Eventually expanding the roster is going to be a negative.

You're not wrong... I could instantly tell you exactly what character people were playing just by the weapon sound, but they've changed every single one of them enough that they don't sound the similar to their old shots. Everything had the bass jacked up to it.