Advantage+ Shopping Campaign (ASC) is indeed designed to scale high-performing creatives, not for testing. Moving only proven winners ensures the algorithm optimizes effectively. However, introducing a small percentage of fresh creatives (while keeping a majority of top performers) can help prevent ad fatigue and maintain long-term performance.
So, the best approach is to prioritize high CTR, strong conversion rate, and healthy ROAS creatives from your prospecting phase, but also gradually test new variations within separate campaigns before adding them to ASC. This keeps your campaign scalable while maintaining consistent results.