Is it ok to remove azure default initiative and use the azure benchmark?

Initiatives are great for applying and managing policies at scale and I always recommend my customers to group policies based on the "intent". The way you group your policies to initiatives has also an impact on reporting (how you see your compliance in the Compliance blade/view).

You should think about your Azure environment and what "standard" you want to apply where and how easy it is to eventually add/remove policies from initiatives, change assignments, etc.