Check it is actually true
Often demand exists under a different name — the problem rather than the product, or a category term you had not considered. The search terms report on a small broad-match test answers this cheaply.
If it really is new
Demand Gen and YouTube create awareness; Search then harvests the category and brand searches that follow. Expect the Search account to grow after the discovery spend, not alongside it.
How to judge it
Not on the discovery campaign’s own ROAS, which will look poor. On total account revenue and on whether branded search volume is rising.