I believe your interlocutor is suggesting that the Tor protocol makes tradeoffs in its design that tend to make it slow. This is demonstrated by slowness in the largest Tor deployment to date.
Also, have a large and single-purpose Tor deployment controlled by a single provider would mean there would be no privacy from that provider and anyone able to send them subpoenas. I think that this weakens the privacy provided to the point where the decision to use Tor at all becomes questionable.
Sure but the goal of such a system is just to distribute content more efficiently so protecting the users from the provider of the system is not the goal, you just want to protect the users from each other, if you like.
In that case, I'm afraid I don't see any advantages over a traditional CDN. Certainly not any privacy advantages, almost certainly not any performance advantages, and probably not any cost advantages either.
Also, have a large and single-purpose Tor deployment controlled by a single provider would mean there would be no privacy from that provider and anyone able to send them subpoenas. I think that this weakens the privacy provided to the point where the decision to use Tor at all becomes questionable.