Navigating Client Hesitance on 1P Audiences in Programmatic Ads

Hi everyone, I've encountered a challenging situation with a client who insists on using their 1st party (1P) audiences despite seeing less-than-ideal performance. While these audiences have decent scale for the current budget and perform adequately in terms of ROAS, they eventually reach a plateau and result in a suboptimal average frequency. After months of discussions, we finally persuaded the client to allocate 10% of the total media budget to lookalike/predictive audiences. We adjusted the settings to significantly increase the audience size, making them quite different from the original seed audiences—about 10 times larger. By adding performance-based targeting, we achieved a 4x ROAS compared to the 1P audiences. Unfortunately, despite these impressive results, the client's CMO still limits non-1P spending to a maximum of 10%. It's frustrating because it feels like we're not being allowed to make the most of our data-driven insights, making our efforts seem somewhat futile. Has anyone been in a similar situation or have any advice on how to navigate this? Thanks in advance!