Shaul’s mother was definitely dina acc to rashi and she was called kenanis because of her union with shechem. Whether like I learned that shaul was born as a result of that union and later adopted by shimon as a step son, or as you suggest that he was from bnei shimon so his father was shimon and he was not born from dina and shechem but later from dina and shimon is unclear. I have no proof either way (in divrei hayomim it writes simply shaul) but that is not my question. I asked why osnat was not included in the 70.
Interestingly the pasuk I brought above says “bnosov” plural. How many daughters went with him to mitzraim besides dina?