It reminds me of The Adventures of Captain Planet and the Planeteers only as far as it names and affects the elements similarly -- certainly not for its story lines. The Power of Heart may be largely absent in AtLA, but it wasn't completely lost, because Aang used something like it in The Swamp, and Guru Patik used the same thing in Appa's Lost Days.

Captain Planet himself is more like the Avatar Spirit, not an avatar. I call Captain Planet a golem (often described as a being taking human form, but without a divinely-granted soul) because he is dormant and hidden until the Planeteers give him the power of the rings. If Captain Planet were more like an avatar, he wouldn't simply disappear to regenerate when his services were no longer compulsory.

I remember an episode where Ma-Ti (Heart) and Kwame (Earth) were trapped on an interplanetary vessel heading toward Planet Venus after the Planeteers had given Captain Planet the power of the rings. Captain Planet tried to return the power after his task was done, but the two boys (and The President [based loosely on President George Herbert Walker Bush]) had already traveled beyond Planet Earth's atmosphere. While the other three children got their ring power back, the two boys didn't. Captain Planet re-formed on Planet Earth, but had fewer colors (white and the colors of Earth and Heart) and their corresponding powers (with Earth, he hits the ground without injury, leaving only a shallow crater, and with Heart, he and Gaia [the Spirit of the Earth] were able to contact Ma-Ti and Kwame as the vessel neared Planet Venus).