Not the first time an aging ex Airtex Chieftain can’t maintain altitude on a single engine
In this case I think it would of had to have some other contributing factor. At such weight after long fuel burn and a single POB it would have to have some serious other drag to prevent it from flying. Considering the issue seems to have started some 10-15 minutes prior to the landing there should have been some radio communication. Apart from the few well known cases where PA31 have failed to perform on one engine there are also many others that have successfully flown on and landed without incident. I've personally had to land one with a feathered prop and it flew fine at medium load, I wouldn't want to test one at max weight on a hot day though...