Even in [Idol Wars] Pre-Reg it's only 1.6% for 5*, but there's constantly SSR flying around the selves because there's the milestone rewards ( which prompt people to make more dupe account )
and xtra pulls from twiiter user.
for [Sengoku] it's harder to get 5* probably because:
1.People are probably being put-off by the paywall.
2.No milestone rewards.
3.only limited to 10 pulls.
put 1,2,3 together and there's less people doing Free Gatcha = Harder to get 5*.
It's like [Shooting Girl] Pre regs, most people got their 4* at the end of the event or none.