If you are going purely for minimizing time, all forms of shared transport will be slower than going it alone. A plane trip on a commercial route is slower than getting a private jet, for example.
The difference is in how much additional time the shared option takes, and how the experience varies, especially relative to cost. For an Amtrak cross-country trip measured in days, I agree with you; I won't ride that (outside of the trip being the reason for the trip) either.
But Amtrak Cascades between Seattle and BC or Portland? I'll definitely take the train for that. I go from downtown to downtown in a bit longer than the time to drive, I don't have to deal with the TSA, I don't have to concentrate on driving myself, I can get food and use the restroom without stopping my trip, and I get a much better seat than on a plane.
If the time comparison is within about 50% extra train versus plane or car, I'm taking the train every time.