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:

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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:

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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--

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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:

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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.