Amtrak owns about 3/4 of the tracks between Boston and DC, so those will be their most reliable. That’s what I use it for the most. From my experience, that’s also more expensive than other trips, but I haven’t done an extensive comparison.
Elsewhere, on tracks that are owned by others, especially commercial companies, Amtrak may not get priority, so things get dicier.
NEC, Surfliner, maybe a few others. All the long distance routes save the auto train would be cancelled leaving only the commuter trains.
If it has sleeper cars, it loses money.
However Amtrak serves a portion of the population that are in areas not serviced by much else and I’m perfectly fine with subsidizing that outright. But that may be because choo choo go choo.
Elsewhere, on tracks that are owned by others, especially commercial companies, Amtrak may not get priority, so things get dicier.