Having a enforced max length on any route especially those with commuter service is not a bad idea, it is the tendency of freight to scale up the number of cars as much as possible for efficiency, passenger services work better shorter with more frequent services.

Yes there are myriad other reasons Amtrak gets delayed, it is not like this is the only bottleneck they have, but that doesn't mean this is not also a key problem.

Amtrak isn't lying. You can see that the freight trains are too long by literally just watching one.

What does Amtrak have to gain by lying about this?

From what people in the industry have told me, freight train management is no less scummy than any other kind of freight transportation management, and they continually make trains longer and longer despite nearly everyone’s objections. Some are miles long so there’s no way engineers can see the front of the train even with a gentle curve, and they’re taking hazardous cargo through populated areas.

I’d take Amtrak’s word on it.

I worked for a freight railroad. Amtrak is correct.