There is a Machloket between Rif and Rambam. The subject is beginning in massechet Brachot. mishna Chapter 3,4.(in Gemara folio 20B)
A BA'AL KERI SAYS THE WORDS [OF THE SHEMA MENTALLY WITHOUT SAYING A BLESSING EITHER BEFORE OR AFTER AT MEALS HE SAYS THE GRACE AFTER, BUT NOT THE GRACE BEFORE. R`JUDAH SAYS: HE SAYS THE GRACE BOTH BEFORE AND AFTER (Soncino)
I will quote the Bartenura on the Mishna concerning baal keri. as an abstract of the Gemara and after this explain through a few lines of Gemara the difference between diverse Rishonim. And at end, i will ask a question about the Chassidic Minhag you refer. Bartenura:
עֶזְרָא תִּקֵּן שֶׁלֹּא יִקְרָא בַּעַל קֶרִי בַּתּוֹרָה בֵּין שֶׁרָאָה קְרִי לְאוֹנְסוֹ בֵּין לִרְצוֹנוֹ עַד שֶׁיִּטְבֹּל. וְלֹא מִפְּנֵי טֻמְאָה וְטָהֳרָה שֶׁאֵין דִּבְרֵי תוֹרָה מְקַבְּלִין טֻמְאָה אֶלָּא כְּדֵי שֶׁלֹּא יִהְיוּ תַּלְמִידֵי חֲכָמִים מְצוּיִין אֵצֶל נְשׁוֹתֵיהֶן כְּתַרְנְגוֹלִים ... וּכְבָר נִפְסְקָה הַהֲלָכָה דְּבִטְּלוּהָ לִטְבִילוּתָא, וּבַעֲלֵי קֶרְיִין קוֹרִין קְרִיאַת שְׁמַע כְּדַרְכָּן וְעוֹסְקִין בַּתּוֹרָה וּמִתְפַּלְּלִין וּמְבָרְכִין כָּל הַבְּרָכוֹת וְאֵין מְעַרְעֵר בַּדָּבָר Ezra enact a law: A with a Status of baal keri. In Tora, this status originally concern uncleanness. See Mishna Kelim 1, 1 (sperm make unclean the person that touches it and the person from witch it originates) The verses cited above in the OP are hilchot Tum'a veTahara. Ezra enact a low linked to this uncleanness. A man after having a seminal issue do not clean himself with Mikve is not entitled to read Torah.
Rabbi Bartenura says that the reason was in order that scholars might not always be with their wives like cocks. We will see that this is an interpretation of the Gemara and not a translation, his source is probably in of 2 Gemarot: the gemara cited bellow that contain the expression "with their wives like cocks, and a Gemara in 22B:
Ezra ordained that a healthy man whose emission is voluntary must immerse in forty se'ahs". He builded a new statement. The legislative intent was to prevent an excessive amount of marital relation in Scholars. But this enactment had been canceled. They are now allowed to learn tora, pray and bless.
In this, the Bartenura follows the conclusions of the Rambam. Gemara 22A
R' Nahman Bar Isaac said: It has become the custom to follow these three elders, … and R' Judah Ben Bathyra in the matter of words of Torah. (see above : R'Judah B`Bathyra used to say: Words of Torah are not susceptible of uncleanness) … etc.… When Ze'iri came [from Palestine], he said: They have abolished the ritual ablution (immersion).Then, the Gemara comment a Berayita that says
A ba'al keri on whom nine kabs of water have been thrown is cleanAnd they debate about the dissemination of this teaching:
The one who taught 'he whispered it' thought that the reason was in order that scholars might not always be with their wives like cocks.The Rif wrote:
איכא מאן דאמר האי דאמרי בטלוה לטבילוטא בין לדברי תורה בין לתפילה ואיכא דאמרי הני מילי לדברי תורה אבל לתפילה צריך בטיבלה ולאו טבילה דווקא אלא רחיצה בט' קבין. וכתב רבינו האי גאון זצ"ל כיון דגמרא ליכא בהאי מילתא נקוט מנהג כל ישראל שכל בעלי קריין אף על פי שאין להם מים אין מתפללים עד שירחצו. The Rif concluded following Rav Hayi Gaon that for prayer the enactment is not annulled and Baal Keri need at least 9 Kabim. But Rabenu Yona and Rambam do not agree and the Shulchan Aruch follows clearly the Rambam that the "Ezra's immersion" was completely cancelled S.A. O.C. 88 But Magen Avrohom, cited in Mishna Brura calls those tha continue the minhag as Anshey maasse (people with a great behavior). This minhag is very good (note that it is a little different from a daily Tevila). {In Gemara, different types of Baal keri are distinguished, and immersion and 9 sea sprinkling, in Rishonim, dinim of Hatsitsa. see in poskim}
Concerning the Chassidic Minhag I have a Kashia on Gemara 22A:
R' Hanina said: They put up a very valuable fence by this, as it has been taught: Once a man enticed a woman to commit an offence and she said to him: Vagabond, have you forty se'ahs to bathe in, and he at once desisted.You says "there are certain Hasidic communities where men go to the mikveh daily". If this scholar was following the "daily mikveh minhag" would he have a reason to desist if anyway tomorrow hi will go to the mikve?