The thing that hurts the low tier girls the most are not the stats, but the drastic lack of abilities (their Ults are weak, and they have only one passive which is usually 1/3 strength of what you get from 5/6*).

I too have a 3* favorite (Sasankua), and thats why I also voted for low tier girls in the DMM popularity poll - so that these girls can get new better versions