Letting alone the "avoid curve", my experience in 300's, while foolishly hovering out of ground effect, taught me that even flying alone, immense amounts of power are used this way.
If two fellows are hovering around on a warm southern day, and lots of attention is being paid to the object of the filming, rather than the power being consumed by the engine, it seems reasonable to expect that the engine might be over taxed. Getting it way too hot, detonating it, sticking or warping valves, and otherwise abusing it, is likely to make it loose power.
Probably not the helicopter's fault, from my point of view...