Daf Yomi Yevamot 79-80: Is The Stam Mishna Really In Accordance With Rabbi Akiva?

We are soon to encounter the following Mishna and gemara in Daf Yomi. Borrowing from my translation at my Rif blog:

{Yevamot 79b}
Mishna:

אמר רבי יהושע שמעתי שהסריס חולץ וחולצין לאשתו והסריס לא חולץ ולא חולצין לאשתו ואין לי לפרש
אמר רבי עקיבא אני אפרש סריס אדם חולץ וחולצין לאשתו שהיתה לו שעת הכושר סריס חמה לא חולץ ולא חולצין לאשתו שלא היתה לו שעת הכושר
ר' אליעזר אומר לא כי אלא סריס חמה חולץ וחולצין לאשתו שיש לו רפואה סריס אדם לא חולץ ולא חולצין לאשתו מפני שאין לו רפואה
העיד ר' יהושע בן בתירא על בן מגוסת שהיה בירושלים סריס אדם ויבמו את אשתו לקיים דברי ר' עקיבא:

Rabbi Yehoshua said: I have heard that a saris {eunuch} performs chalitza, and they perform chalitza for his wife, and also that a saris does not perform chalitza and they do not perform chalitza for his wife, and I do not have an explanation.
Rabbi Akiva said: I will explain it. A eunuch at the hands of man performs chalitza and they perform chalitza for his wife, because he had a time of validity. A eunuch of the sun {that it, a natural eunuch} does not perform chalitza and they do not perform chalitza for his wife, for he did not have a time of validity.
Rabbi Eliezer says: Not so, but rather a eunuch of the sun performs chalitza and they perform chalitza for his wife, for he has a possible cure. A eunuch at the hands of man does not perform chalitza and they do not perform chalitza for his wife, for he has no cure.
Rabbi Yehoshua ben Beteira testified regarding Ben Megosat, who was a man-made eunuch living in Yerushalayim, that they performed yibbum on his wife, thus fulfilling {/confirming} the words of Rabbi Akiva.

So we have this dispute, but who do we rule like? Well, we then encounter:

{Yevamot 79b}
Mishna:

הסריס לא חולץ ולא מייבם וכן אילונית לא חולצת ולא מתיבמת
הסריס שחלץ ליבמתו לא פסלה
בעלה פסלה מפני שבעילתו בעילת זנות וכן אילונית שחלצו לה אחין לא פסלוה בעלוה פסלוה מפני שבעילתן בעילת זנות:

A eunuch does not perform chalitza nor yibbum, and so too an aylonit does not undergo chalitza nor yibbum.
A eunuch who performed chalitza on his yevama {sister-in-law} does not invalidate her. If he had intercourse with her, he invalidated her, for his intercourse was an intercourse of harlotry.
And so too an aylonit upon whom the brothers performed chalitza, they do not invalidate her, but if they {one of them} had intercourse with her, they invalidate her, because their intercourse is an intercourse of harlotry.

{Yevamot 80b}
Gemara:

קתני סריס דומיא דאילונית מה אילונית בידי שמים אף סריס בידי שמים אבל בידי אדם חולץ
וסתמא כר' עקיבא דאמר בידי אדם אין בידי שמים לא
שמעינן מינה דהלכתא כר"ע דהוה ליה מחלוקת ואח"כ סתם וקי"ל מחלוקת ואח"כ סתם הלכה כסתם:

The Mishna taught a eunuch similar to an aylonit -- just as an aylonit is {so} at the hands of Heaven, so too the eunuch from the hands of Heaven. However, if at the hands of man, he does perform chalitza.
And the plain Mishna is thus in accordance with Rabbi Akiva who said that {a eunuch} in the hands of man, yes, but in the hands of Heaven, no.
We deduce from this that the halacha is like Rabbi Akiva, for this is a dispute {in the Mishna} followed by a plain statement {without dispute}, and we have established that a dispute followed by a plain statement, the halacha is like the plain statement.

Thus, for the aforementioned reason given by the setama digmara, we rule in accordance with Rabbi Akiva.

I find that gemara a tad difficult. After all, the very next Mishna has no compunction about specifying exactly which type of eunuch is under discussion:

{Yevamot 81a}
Mishna:

סריס חמה כהן שנשא בת ישראל מאכילה בתרומה

A kohen who is a eunuch of the sun who married the daughter of an Israelite, he may feed her teruma.

and had Rabbi wished, he could have specified in the previous Mishna as well. Instead, the setama is forced to resort to the fact that it lists saris and aylonit, and thus deduce that they must be of the same type -- natural -- and then continue deducing from there that it is a stam Mishna like Rabbi Akiva, so we rule like him.

But the role of this Mishna seems different to me. I would have said that the Mishna is deliberately not specifying the type of saris, so as to work within the framework of the preceding Mishna. Thus, it does not specify e.g. seris chama so as not to take sides, but rather whichever of the aforementioned we paskin like, that is the saris under discussion. Thus, the stam Mishna is not in accordance with anyone.

On the other hand, there is another reason to rule in accordance with Rabbi Akiva. All else being equal, we have the testimony of Rabbi Yehoshua ben Beteira that actual practiced halacha was practiced and ruled in accordance with the understanding of Rabbi Akiva.