What is the meaning of the words כהיום הזה in the prayer על הניסים ? Are there options other than the Artscroll interpretation, "unquestionable clarity"?
It means "[just] like this day".
The Tehillat HaShem Siddur translates it as:
"...and effected a great deliverance and redemption for Your people to this very day."
I went over the paragraph three times before my answer dawned on me.
It says "CHayom Hazeh" and then says "Achar ken"
This "Achar ken", could be referring to the entire previous statements, or it could be referring to the initial previous statement.
I think, that in this case, it is referring to the "c'Hayom Hazeh".
The battles before Chanukah, where indeed miraculous, and Hashem gave a great redemption and salvation, and performed great wonders for the small Jewish Army.
However, that "Tshuah" and "perkan" did not last very long, and it was not always clear. The Jewish people were still divided, and needed allies for foreign nations. It was not until 10-20 years later that independence was achieved. And then, only 1 to 4 generations later, sovereignty was lost again.
However, On that day, which we celebrate as "this day", (i.e Chanukah) is when the Jewish people and leaders felt the victory of few against the many etc etc, Yeshuah and Pirkan were clear and evident to everybody, and we pray and give thanks for what "little oil" we were able to find during those times.
So in short, "k'Hayom Hazeh" means "Like this day (When the victories were apparent)", which is then contrasted with an "afterward" which focuses only on the dedication of the Beit Hamikdash and ignore the battles and hardships that came to the Jewish people aftwards during that time.