Hello Philip!
I hope you are fine.
This question does not have a definitive answer because both SEO and advertising can be useful based on the needs of the project.
If the employer wants to achieve a desired result in a short period of time, advertising is considered a more valuable option than SEO, but sometimes the employer does not have time and his desire is to obtain the expected results in a longer period of time. In this case, SEO is a better option than advertising.
Do not forget that SEO is almost free, or to increase the traffic of a website, SEO will cost much less than advertising.