Note that the Northeast Corridor, the only thing approaching high speed rail in the US, is very profitable. Unfortunately Amtrak then has to take that surplus to subsidize unprofitable routes elsewhere.
But of course that's a complex issue, some say that the local service degraded as more resources were diverted to the TGV lines. I can't really imagine that having the center of Marseille 3 hours away from the center of Paris can be a net negative overall. It beats the plane every time, that's for sure.
The high speed train stops right in the city center.
So unless one of your endpoints is close to one of the airports it's 3 hours for both of them.
Also in my experience the TGV is much more comfortable than similarly priced airplane tickets. You can look at the landscape (unless you're traveling by night), you have more room, you can walk around etc...