How does Shakespeare establish the dignity and heroism of Othello early in the play, and does he regain his stature in the end? How?

In Acts I and V of Othello, Shakespeare gives Othello dignity and heroic words, but in Acts II, III, and IV he gives Othello ignoble and immoral actions.  Overall, Othello wins a battle with words but loses the war overall.  As such, he is no hero--only a tragic one.

In Act I, Othello defeats Brabantio's, Iago's, and Roderigo's plans to annul his marriage, place him in prison, and do him physical harm.  How does he win?  Using his words, and not using his hands.  On the street, he talks Brabantio's men--who have him outnumbered--out of fighting.  He says:

Hold your hands,
Both you of my inclining, and the rest:
Were it my cue to fight, I should have known it Without a prompter.

Later, in the Senate with the Duke, he likewise wins Desdemona's hand by using powerful rhetoric:

Her father loved me; oft invited me;
Still question'd me the story of my life,
From year to year, the battles, sieges, fortunes,
That I have passed.

--and--

When I did speak of some distressful stroke
That my youth suffer'd. My story being done,
She gave me for my pains a world of sighs:
She swore, in faith, twas strange, 'twas passing strange,
'Twas pitiful, 'twas wondrous pitiful:

Just as Othello used stories to win over Brabantio and Desdemona, so too does he use a story to win over the Duke, the Senate, and us.  The marriage is condoned, Othello is commissioned to Cyprus, and Desdemona may accompany her husband on the honeymoon.  At this point in the play, Othello looks like a hero.  But wait...

In Acts II-IV, Othello loses his power of language.  He is like Sampson with his hair cut off: powerless.  He suffers seizures, rage, fits of jealousy, misogyny.  He slaps Desdemona publicly, slanders her name, murders her, aligns himself with a villain, and shows little remorse for his crimes.  Listen to the once mighty Othello now:

Pish! Noses, ears, and lips.
--Is't possible?--Confess--handkerchief!--O devil!--

He's a stuttering, powerless fool.  Iago-the spider-has Othello-the fly-trapped in his web of deceit and jealousy.  Iago is a puppet-master and Othello now dangles on his strings.  Othello is a green-eyed monster.  A beast.  A slave.

In Act V, Othello tries to resurrect his reputation, but it's all for show.  He knows that he is ignoble, immoral, a misogynist, and a murderer.  His last monologue about doing the state "some service" is all lip service.  He still only focuses on himself.  He makes no confession or prayer regarding the two women who lie dead on the bed.  He does not honor them, only himself.

No, Othello suffers too much pride to become heroic.  He only seems heroic with his words.