Fomrulation matters for cosmetics, but not for prescription creams?

I am not sure if this is the right place to post. I wanted to ask for your opinion. I hear a lot online recently that "formula is king" and ingredient lists don't matter, but the whole formulation does, and you can't judge a product from an ingredient list (seeing a lot of posts on instagram mostly). I get it, but am also wondering: I've never heard that a specific formulation for a tretinoin cream matters. It's only percentages. The same for other topical prescriptions: it's just the percentage of the active. So what's the deal?