Mega Heracross isn't rubbish, it's equal! but in different areas :P. He has a decent speed output and can be useful, below is an example of why it could be better than Mega Pinsir but lacks major speed clauses in it's replacement. (I run both and both are equally indifferent to each other). Sticky web would give it a boost but again like mentioned below with just 95 speed it could outspeed most anyway.
Base Stats as mega:-
Heracross-MegaBugFightingSkill LinkHP 80Atk/185Def/115SpA/40SpD/105Spe/75BST/60
Lv 50 Mega Heracross:-
Hold - Heracrossonite
Ability - (as Mega) Skill LInk
Bullet Seed
Pin Missile
Swords Dance
Brick Break
Ev's Preffered - 252 HP/252 Attack/ 4 Speed Adamant Nature - Attack+ Sp.atk-
So at lv 50 as Mega Heracross has:-
HP - 187
Att - 260
Def - 135
Sp.Atk - 54
Sp.Def - 126
Spe - 95
95 Speed beats most Pokemon on wi-fi battling.
Source - Exp.