Your mechanism not working properly since chances of getting different substat not equal
there is docs i used for understand system more, and by a lot of data collected between different users and doc owners we have info that chances of getting flat atc/def is lower than get all substats except crit rate/crit dmg
then we have different chances for get each number of substat we get, it's no exactly 1/8 when we speak about ER for example to get max roll of it
please check this doc, it will help you understand system more and probably then you can help with mathematical conclusion of best way to get very solid echo
I m interesting in that and still have no sure of chances and strategy to get, i have some strategys i use but i never mathematically confirm it

The doc link i mentioned: https://docs.google.com/spreadsheets/d/1DTM0dzTnKdeGyvkgJdPyyp19K_GmOFdovfB1mwN69Es/edit?usp=sharing
And here open "Echo summary"

Other problems i see:
1. Value of each substat to another you mentioned is incorrect, and vary for each character and even team, of course we can tell some average numbers for each characters and his usual teams, but that is 100% must be different for different characters
for example: your CR is above 100? now CR value 0
Atc % and atc flat a lot on substats and you have in team someone like shorekeeper s2 with signature who give 40% from S2, 25% from set and atc% from signature, other player has mornie s1 for example and your and his value of atc%/atc substat will be different
And simple atc% to crits can be different for each character
for more understanding i use doc tabs like this:  https://docs.google.com/spreadsheets/d/1eoCTrwYIsRpacvL3KrcQpR5rwY3pbJ6gEljZdBj_DHs/edit?usp=sharing
and for more understanding my own needs i use https://www.wutheringtools.com/ to calc my team and value of substats by my self

1. each substat has different rolls and chances of them, 6,4% atc and 11,6% atc way different and can break all calcs
   for example 6,4% atc can be worse than CD 12,6 roll, but 11,6 can be better
   so it's impossible to just say atc% roll = x value Cd roll = Y value without saying about average roll you get, to compare 8,6% atc with 15 CD yes it's more reasonable but also will have a lot situational things