I'll have to throw my 2 cents in since I taught barrel rolls as an Air Force instructor pilot in T-37s many years ago.

The maneuver is a spiral in the sky. The differences are in the instruction. As for it being a 1g maneuver, as an engineer, I question that. If you pull up, you are pulling more than 1g. Maybe not much more, but slightly more. The tighter and faster the roll, the more gs you'll pull.

As for the "spot on the canopy" vs. other methods, they result in the same maneuver when viewed from outside the airplane. I always found that students had a harder time learning the "spot on the canopy" technique so I tended to teach the maneuver using section lines or roads.

You picked out a road and dived on it to gain airspeed. Then you turned off to one side 30 degrees (or whatever amount you wanted). You started a gentle, rolling pull-up, continuing over to inverted. You watched the road and timed the roll so when you were on the horizon inverted you were 30 degrees off to the opposite side of the road. You continued the roll and gentle pull to place the airplane upright back over your original 30 degree line.

If the student had great difficulty, I used a crossroads and a 45 degree turn off. I had him line up between the 90 deg. angle formed by 2 crossing roads, then turn off to one road. He would fly inverted to the other road, then back to the original one. This gave a huge barrel roll, but it was easier for the slower students to visualize.

What you are seeing with the arco teams is a berreled out version of an aileron roll. In ful scale planes (competition acro planes excepted) you keep 1 g to stay in the seat so aileron rolls tend to look slightly barrel. In a formation roll, which I have done in several airplanes, the leader keeps slightly over 1 g so the wing men have an easier time staying in position. Otherwise, the inboard wing man would be using negative gs.

We generally don't do barrel rolls in RC since they, of necessity, cover 3 dimensions and are hard to judge. Viewed from the side, how far out was the plane in inverted? Hard to see.

Hope this helps.