An observation, not a legal opinion: Despite the broadness of the "accrual of flight time is compensation" language seen in some of the FAA Chief Counsel material, when actually applied there is typically some other element of compensation to someone or something else that either makes the operation "look" commercial or the "flight time" not the only compensation in the picture.
You can actually see it if your read the Chief Counsel opinions on the subject.
In 1990 there was the Lincoln letter where the FAA said a glider tow pilot was receiving "flight time" compensation. But the pilot was also getting free use of the two plane and the towed pilots were paying a fee to someone for the towing. (There was a reg change to take care of this one)
In 2006 there was the Bobertz Letter where the FAA said a pilot making numerous trips to transport the members of a racing club implicated the "flight time as compensation" rule. But in that one, the pilot was also charging the passengers their pro rata share (with no real common purpose except for maybe the first trip) and the "flight time compensation" rule discussion is almost an afterthought.
In 2013, there's the Howell Letter where the question was about a private pilot doing airshow work, the FAA goes back to its 1990 roots with the language "the logging of flight time is compensation if the pilot does not have to pay the costs of operating the aircraft."
I don't think the free airplane is a requirement to find flight time compensation but it looks like there's got to be some element other than simple taking a friend for a ride.
But it definitely is a problematic doctrine for one trying to understand it. The other equally nasty one is "business goodwill" as compensation, which I think is even a bigger potential problem.