The bulk of this is simply not correct, and the rest is misleading. Taproot USDT volume on the lightning network will be primarily repeat cross-border transactions between parties that know each other, which is how it is on tron. These parties will have directly connected nodes, and therefore zero routing fees. However these transacting pairs will be regularly popping in and out of existence, with on-chain transactions each time.

Then you can ask why is lightning attractive to USDT people already using tron, and for the answer to that you again have to understand the world of tether and what the motivations are in that world and the drawbacks of tron. but sufficed to say it's quite attractive.

The part about this not being in the original sermon for bitcoin, sure that's true, but again, it is what it is.