Even with the new CDN path, there are ways to determine; like the DNS CNAME setting as a big hint. Why hide it? I would think Webflow offers more confidence as a hosting partner than “name your agency”. Sell your markup or final price as a value add. I do. I have had no pushback.
If clients what to pay direct, let them, but then they can maintain settings and handle support issues right? It’s like when I spin up and maintain AWS servers for clients. They pay me a monthly fee well over and above my costs and they know exactly what I provide for it. Expertise and a single point of contact. That is gold.