As a genetics and genomics editor, I frequently deal with large author groups with multiple author roles. To keep the peace, I have learned to allow a single equality group and also a single statement that "these authors equally supervised" the work. We have recently had to remove the [Equal/Leading/Supporting] pull-down list for quantifying the CRediT terms.
Instead: why not have two options on a pull-down Equal or [blank (default)]
This would prevent a new round of discussion by authors as they wrangle for position in the linear order of authors and dealing with multiple contributions. A journal could implement either the three option list or the two option list (or all four if they were so inclined).
I guess that Equal refers to the significance, not the amount of the work.