Not getting same day dispatch date for SELLER FLEX ORDERS

What is the point of shifting to seller flex if we are not getting same day dispatch date ? We have some skus in prime and they get same day dispatch. Our orders are affected due to late delivery. What can be done ? we tried raising tickets but they give same response that its all dynamic based and it will be automatically allotted. Even during festive days our orders get dispatched late and main earning opportunity is lost.