״וְהָיָה ה׳ לְמֶלֶךְ עַל כׇּל הָאָרֶץ בַּיּוֹם הַהוּא יִהְיֶה ה׳ אֶחָד וּשְׁמוֹ אֶחָד״. אַטּוּ הָאִידָּנָא לָאו אֶחָד הוּא? אָמַר רַבִּי אַחָא בַּר חֲנִינָא: לֹא כָּעוֹלָם הַזֶּה הָעוֹלָם הַבָּא. הָעוֹלָם הַזֶּה, עַל בְּשׂוֹרוֹת טוֹבוֹת אוֹמֵר: ״בָּרוּךְ הַטּוֹב וְהַמֵּטִיב״, וְעַל בְּשׂוֹרוֹת רָעוֹת אוֹמֵר: ״בָּרוּךְ דַּיַּין הָאֱמֶת״. לָעוֹלָם הַבָּא, כּוּלּוֹ ״הַטּוֹב וְהַמֵּטִיב״.
"And the Hashem shall be King over all the earth, on that day shall Hashem be one and His name one” (Zechariah 14:9). Is that to say that now He is not one? Rabbi Aḥa bar Ḥanina said: The World-to-Come is not like this world. In this world, upon good tidings one recites: Blessed…Who is good and does good, and over bad tidings one recites: Blessed…the true Judge. In the World-to-Come it will always be: Blessed…Who is good and does good.
I get the general impression that this gemara is trying to demonstrate that Hashem not being One, so to speak, just means we can't perceive Him in the bad things that happen in life, which means we don't see Him in everything, and therefore it seems as if He is not One, ch'v.
So, it seems that the only way for this proof to work properly is that it is implying that there will indeed be "bad tidings" in Olam Haba, e.g. cancer(?), however in Olam Haba, we will not perceive it as bad in any way, but actually just see it as כֻּלּוֹ טוֹב (Kiddushin 39b which implies that there won't be things like accidents or death in Olam Haba!).
If it just means that in Olam Haba there won't be cancer, then that implies that Hashem actually isn't One now, ch'v? If you want to resolve it by saying that it means we will retroactively look at historic cancer with a good light, then what's the point of centering this discussion about berachot? We won't be able to say הַטּוֹב וְהַמֵּטִיב on cancer, ever, it's just theoretical (we are not allowed to say it now, and Ben Yehoyada seems to imply that there will not be things like cancer, and therefore I am not sure if he is answering this kashe or not).
This seems like an obvious question, I am sure it is dealt with somewhere, has anyone seen an answer to this?