If I, working there, found that FB was painful to work with, I'd go somewhere else, as simple as that. I won't spend two days wrestling with FB to see if my ad it's ok or not.

I may not care for political advertising, since my client is not looking to "make a profit" like a traditional customer. But I definitely do for an eCommerce brand for example.

Most agencies use FB because it's easy to work with and it's cheapish with a little expertise. If that dissapeares then nobody is goung to pour money on it.