IMO, it should go even lower as Heliolisk outclasses it pretty hard. It has worse Speed and Sp.Atk (barely, but still), no Sp.Def (neither are supposed to be taking hits, but Heliolisk might actually survive a whack or two).
-Both have an ability that gives them an immunity, sure. But there's really 4 Electric types in UU: Galvantula both that outspeeds and is usually Sash so Overheat doesn't even kill; the standard LO Heliolisk outspeeds and has a 50% chance to OHKO with Hyper Voice if rocks aren't up; Mega Ampharos is Mega Ampharos; Mane can't scratch Rotom-Heat, it only inconveniences it if it's Choiced.
Meanwhile, Heliolisk's Dry Skin helps against Blastoise, Empoleon, SD Feraligatr, Milotic, Slowking and Tentacruel, while it completely shuts down Crocune and Vaporeon. And I guess it's neat if you've got a Mega 'pert around.
-When it comes to movepools, Mane only has STABs, Fire moves and Hidden Power. Fire only really helps with Mega Obama, Chesnaught, Doublade, Forretress, Heracross, Roserade, Manectric. Meanwhile, Heliolisk has the choice between 2 STABs, Surf, Grass Knot, Focus Blast and Dark Pulse.