Though I think that if Warcraft III's unit/structure game was more focused on macro management and heroes were more focused on micro management it would have made the gameplay a little more fun. To me that sounds like the perfect balance, and since heroes are naturally capable of doing incredible things, it wouldn't be too unrealistic that a well managed hero could do a lot to a macro managed team of units. It isn't very worthwhile talking about the game mechanics of Warcraft III though, Starcraft II being out and all.
Warcraft III had races that required a lot of macro if you played in solo queue (Humans and UD def). They also had a bunch of heroes that could carry a team without any units if crept properly. Let me tell you some:
Human
Mountain King - Paladin (imba)
Mountain King - Paladin - Blood Mage (impossible to lose to undead)
Mountain King - Blood Mage (int heroes go bb)
Blood Mage - Mountain King (mass mana on MK or mass dmg on focus fire)
Archmage - Mountain King - Paladin (extra units plus mana aura plus heals and stuns)
Archmage - Mountain King - Blood Mage (unlimited mana supply for MK, water elementals, and super powered nukes)
Archmage - Paladin - Blood Mage (never die + undead focus fire to the max)
Night Elf (Can't list every single combo because there are literally thousands of NE combos out there)
Demon Hunter - Panda (superman + aoe)
Demon Hunter - Dark Ranger (superman + silence)
Demon Hunter - Tinker (superman + exploding robots)
Demon Hunter - Beastmaster (superman + slow poison summons who can see invis BM)
Demon Hunter - Beastmaster - Tinker (superman + slow poison + exploding robots)
Warden (strongest ult, easy to level, best nukes in game)
Warden - Panda (strongest nukers in the game)
Kotg (with mass hunts if you can keep him from dying and keep a substantial mana pool you can end the game in 6 minutes)
Firelord (strongest hero early game only applicable to NE)
Orc
Blademaster - Shadow Hunter (best hero in game + a disable and a heal)
Blademaster - Tauren Chieftain (best hero in game + an aoe stun and a speed aura)
(that's all for Orc. Notice a recurring theme? if you can play your Blademaster well you automatically win all matchups)
Undead
Death Knight - Lich - Crypt Lord (best tri-hero in game. 300 dmg nuke + 300 dmg aoe nuke + 200 dmg line stun)
Death Knight - Lich - Drow Ranger (same as above but replace stun with silence)
Death Knight - Dreadlord - Lich (gosu surrounds)
Death Knight - Dreadlod - Drow Ranger (gosu surrounds + silence on Warden. haha that little scumbag dies)
These are all basically hero combinations that if you micro well enough you'll win. People who think that heroes can't be well played enough to carry a game generally play 3v3/4v4 RT and are used to massing a bunch of shitty tauren and knights to win.