you’re ignoring the root etymology of the word

Thousands of times a day for me, you don't know the haff of it.

The word has always had a t sound since Old English, and it's part of the reconstructed language Proto-Germanic in the form *ufta. Every other Germanic language displays a t in the corresponding word:

Scots oftin (“often”), North Frisian oftem (“often”), Saterland Frisian oafte (“often”), German oft (“often”), Pennsylvania German oft (“often”), Danish ofte (“often”), Norwegian Bokmål ofte (“often”), Norwegian Nynorsk ofte (“often”), Swedish ofta (“often”), and Icelandic oft (“often”).

Source

So, the dictionary is not a gold-standard.

It is, in fact, the opposite and in very simplified terms, just a book of how people currently pronounce words and their meaning today. Think of it more as a record book for the time it was printed, rather than a rule book; living languages are funny like that.

If you would like to know more, I highly recommend Word by Word written by Kory Stamper, one of the editors for the Merriam-Websters Dictionary.

That's how I feel about helicopter!