Wouldn't one try to increase the Ad Budget by some % of the incremental Outcome-Based modeling (OR: spend the same Budget and move to Outcome-Based modeling for higher ROAS)... since IF you invest the total incremental gain (ROAS) wouldn't that conceptual

What I had in mind was marginal utility analysis from economics. If your ROAS target is $2.20 and your advertising generates $3.30, you have a surplus that can be reinvested in additional advertising. At some point the marginal yield will start declining. But even as you get to $2.50, $2.40, $2.30...you are still above your target.  The result of this is a higher ad budget with more sales, representing growth at a desired level of profitability.