>>> evaluated in real-time for their cost to conversion ratio
We tried that in the past, but our business (mostly OTP for banks) do not allow any margin of error at all. The thing is that we would get positive delivery reports which were fake.
We also tried some 3rd party testing tools (Testelium[1], TestMySMS[2], etc) but again, our hacky upstream providers were ahead of us and they would put those test number in white-list so that everything would look just fine when testing.
At the end, we settled for direct or 1-hop connection. Margins are tight, but this is the only way to offer a high quality service.
Of course, YMMV