Zhuge Liang was an over-idealistic individual like Liu Bei who believed in restoring something that was broken. He had some contributions and stuff but also had his shortcomings, equating him to a mere mortal, HOWEVER, he was worshipped by later chinese like a deity which I cannot understand. And most importantly, why was he viewed as a hero? Who is he hero to?
Personal grumblings aside, if Zhuge Liang's to be viewed as a hero, the safest way to do it is from the perspective of Shu and Wu. Attack from the points that he did a lot to forge the alliance between Shu and Wu during the battle of Chi Bi and compare his greatness with Zhou Yu's pettiness. The victory of Liu Bei and Sun Quan over Cao Cao in this crucial battle ensured Liu Bei's survival, hence he was able to expand his empire to Jingzhou and Yizhou in the later years.
Then also, talk about Zhuge Liang freeing Meng Huo 7 times, instead of executing him. This show of mercy led Meng Huo to believe in his benevolence and as a result, the Nanman submitted not due to force, but because they were convinced of Zhuge Liang's leadership.
Then you may talk about his northern campaigns. Zhuge Liang though foolhardy and ill-luck, marched his troops numerous times in his crusade against the evil Wei and Sima Yi. He died in his attempt, a show of tremendous loyalty to his empire.
Also, why was he a hero of three kingdoms? He had a vision which he shared with Liu Bei that the empire could be split into 3 portions. He assisted Liu Bei to gain one of the three. With his death, Shu (or the good guys' camp) fell in no time, hence, Zhuge Liang was "responsible for maintaining the balance in the three kingdoms", therefore, he is a hero of the three kingdoms.