What kind of assistance can another aircraft provide to an incapacitated pilot?
This is speculative and I haven't looked at the links you gave, but I can think of a few things:

Having another aircraft there gives ATC a way to gather information that they otherwise couldn't. For example, if the second pilot had observed that the 'incapacitated' pilot was actually awake and alert and there was a second person in the cockpit brandishing a gun, I think it's safe to assume that the response from ATC, law enforcement and the military would have been different.
The worst case is that the incapacitated pilot never recovered and simply crashed. In that case the second pilot could give ATC a precise location for rescuers, which could be important in a more remote area. Especially if ATC had no radar coverage.
The incapacitated pilot could have recovered but still been disorientated and unable to communicate properly. It's possible that the second pilot could have led them to a nearby airfield. That would still require some understanding and communication between them, and the second pilot might not have been comfortable with doing it, but it's an option.
It's possible that the incapacitated pilot recovered but couldn't talk directly with ATC. That could be because they drifted down to an altitude below ATC's radio coverage, or couldn't change frequencies, or whatever. The second pilot could relay calls from ATC in that case, assuming that they could work out which frequency the incapacitated pilot was on. Relaying calls from ATC to another aircraft is fairly common.

I'm sure we could all come up with other ideas, but I think the first point is the most important: when something strange is happening then it's best to gather as much information as possible.