Why are new 5*s being mixed with two others in the vault when they are first released? Now that they are required in pve, they should be made easier to get, not made harder.
Even if they are alone, it won’t be easier to get. By themselves, they will still have 5% chance. The extra 10% comes from having the other two 5s. Without them, those 5s pulls would have been more 4*s
Previously, before they added the fillers you got a 10% chance of the new character, so while your chance of a 5* was lower than usual you would at least have a higher chance of getting the new one.
Chalk up the change to another one in the long line of idiocy where RNG is considered to be a good idea for endgame progression. 
Fixed that for you.
I went 1/25 and 0/40 when they had the “10% chance” stores.. That second time d3 decided that wasnt really normal and gave me one for my troubles… anyway, in the end it doesnt matter all that much, what the percentages are on such “small” sample sizes..
and as said before, i rather get better chance of 5s. I prefer 15% of any of 3 over 10% on 1..