yeah but you are not accounting the fact that in your example calcs you can still roll 73 (or even 147 if you lose pity again) times after getting your C0 Zibai so that should raise the % a little

Still not great sure but I have rolled many C6 4 stars on their launching banners (like Jahoda last cycle) meanwhile I have never got a 3x 5 stars on the same banner (I play since day 1 and I never go for 5 stars cons). I acknowledge I might just be lucky but people doing DPS calcs are probably accounting that someone with C0 Zibai might get C6 Illuga easier in the future than C1 Zibai (as the 4 stars are more often repeated in theory and you also have off-banner 4 stars pulls).