- The final verdict of YK is based on weighing one's merits vs sins and not how hard one davens on Yom Kippur. (Rambam Hichot Teshuva 3, 4):
"עָשָׂה מִצְוָה אַחַת הֲרֵי הִכְרִיעַ אֶת עַצְמוֹ וְאֶת כָּל הָעוֹלָם כֻּלּוֹ לְכַף זְכוּת וְגָרַם לוֹ וְלָהֶם תְּשׁוּעָה וְהַצָּלָה שֶׁנֶּאֱמַר (משלי י כה) "וְצַדִּיק יְסוֹד עוֹלָם" זֶה שֶׁצָּדַק הִכְרִיעַ אֶת כָּל הָעוֹלָם לִזְכוּת וְהִצִּילוֹ. וּמִפְּנֵי עִנְיָן זֶה נָהֲגוּ כָּל בֵּית יִשְׂרָאֵל לְהַרְבּוֹת בִּצְדָקָה וּבְמַעֲשִׂים טוֹבִים וְלַעֲסֹק בְּמִצְוֹת מֵרֹאשׁ הַשָּׁנָה וְעַד יוֹם הַכִּפּוּרִים יֶתֶר מִכָּל הַשָּׁנָה."
As Rambam says earlier, YK is dedicated for Beynonim, i.g. those whose merits equal to sins. My logic says that the whole YK day must be dedicated to maximizing one's merits thru performing as many Mitzvot as one can, just as Rambam prescribes for the 10 days of repentance.
Mihsna Peah 1:1 claims that the Torah Study is the greatest Mitzvah of them all (eqalling all the Mitzvos combined!). So the ideal solution would be engaging in learning Torah all day long, similar to Shvuos Night.
Instead, we do "nothing Halachicly valuable" on Yom Kippur, besides the [one-time] Mitzvah of Viduy (Teshuvah) and Teffila (as for Rambam). No obligatory Torah study, no Tzedaka on YK, no procreation etc.
So Why we don't try to maximize our merits on Yom Kippur through engaging in Mitzvot and Torah learning?
NB: Do you think opening a Kolel "Yom Kippur Torah" for those who can't daven for 6 hours straight is a viable option?