PeerTube scales by increasing the amount of instances available. But you are pretty much correct. The two things that's expensive is: Storage and transcoding. The biggest expense is storage. It gets more and more expensive as videos is uploaded. Transcoding can become more expensive, if you have to keep up with new videos getting added all the time.
I would like to see individual content creators create their own PeerTube servers and thereby serving their content to the rest of the PeerTube servers and the Fediverse. I imagine a lot of content creators keep some kind of backup of their videos, so why not attach a PeerTube server to it? PeerTube allows you to keep the original file.
Regarding financial incentive, the "only" thing creators would miss out on, on Peertube is ad revenue. If we disregard the low amount of viewers on PeerTube compared to YouTube, a creator can still use sponsors, patreon, donations, affiliate links etc. on their videos.
You are thinking about channel membership, right? This is something that could also be implemented in PeerTube, either by Framasoft themselves (devs of PeerTube) or as a plugin by anyone.
You mentioned LTT. They have their own video platform. It would have been cool if they had actually used PeerTube and build upon that instead of creating yet another "walled" video platform.