As i see it there is 2 ways that the rolling sustem works
Firstly the odds between Legend, Elite, Ordinary and Slimes.
Secondly the odds between each specific Legendary hero should a Legendary hero pop up.
Now, if IGG were to increase the odds of each individual Legendary hero their profits would drop. So i doubt this is an avenue they would take.
However, increasing the chances of a Legendary hero showing up wouldnt drain profits (as much) as people would still buy knowing the chance is higher.
I think people would be happier rolling Legends more frequently than raising the odds of a specific hero.
The more times you see the purple show up the happier you get.