Multitude, Majority, and Lectio Difficilior

The last verse in Megillat Esther is (Esther 10:3)

ג כִּי מָרְדֳּכַי הַיְּהוּדִי, מִשְׁנֶה לַמֶּלֶךְ אֲחַשְׁוֵרוֹשׁ, וְגָדוֹל לַיְּהוּדִים, וְרָצוּי לְרֹב אֶחָיו--דֹּרֵשׁ טוֹב לְעַמּוֹ, וְדֹבֵר שָׁלוֹם לְכָל-זַרְעוֹ.

3 For Mordecai the Jew was next unto king Ahasuerus, and great among the Jews, and accepted of the multitude of his brethren; seeking the good of his people and speaking peace to all his seed. {P}

Rov usually means majority, and so Rashi explains that since Mordechai became close to the government, he reduced the time he spent studying Torah, and so his colleagues on the Sanhedrin distanced themselves from him. Of course, Rashi here is dealing in midrash, as he often does and seems even more prone to do in the Megillah. The root rbb means myriads, or multitudes, or the many, and this is what is meant here on a pshat level, and what is reflected in the English translation above. (Also earlier, regarding Haman's children, in Esther 5:11):

יא וַיְסַפֵּר לָהֶם הָמָן אֶת-כְּבוֹד עָשְׁרוֹ, וְרֹב בָּנָיו; וְאֵת כָּל-אֲשֶׁר גִּדְּלוֹ הַמֶּלֶךְ וְאֵת אֲשֶׁר נִשְּׂאוֹ, עַל-הַשָּׂרִים וְעַבְדֵי הַמֶּלֶךְ.

11 And Haman recounted unto them the glory of his riches, and the multitude of his children, and everything as to how the king had promoted him, and how he had advanced him above the princes and servants of the king.

There is a tendency to understand rov as majority rather than multitude when you encounter it, because that is its more common meaning.

In Nishmat, which we say on Shabbat and Yom Tov after Az Yashir, there are two versions of the text. One has HaMehulal BeRov HaTishbachot {Who is extolled through a multitude of praises}, and the other has HaMehulal BeChol HaTishbachot {Who is extolled through all of the praises}. Of the two, which is the more original, and thus, more likely correct?

There is a principle often used to determine this called lectio difficilior - the difficult word. That is, the seemingly more difficult word is the more original. This is because one would have an inclination to emend the text to correct it from a more difficult reading to an easier one, but one would not have an inclination in the opposite direction.

Probably, what happened here is that the original was HaMehulal BeRov HaTishbachot. Someone objected, saying: How can you say that Hashem is extolled only through the majority of praises. He is God, so he should be praised through all praises. To say otherwise is heresy! As a result, they corrected the text to HaMehulal BeChol HaTishbachot.

In answer to why Hashem is only praised with the majority of praises, He is actually praised with the multitude of praises.