As a historical fun fact, before 1946, Japanese kana spelling was actually way more confusing. For example, きょう was spelled けふ, とうきょう was spelled とうきやう, かし was spelled くわし, etc., etc, despite the pronunciation being the same as the current one. In 1946 they introduced the modern largely phonetic spelling, although some exceptions were made. The particles は, へ and を were deemed too common to change so they keep their older spelling.
Agreed. This is not technically a word so when asked for a reading the phonetic reading should be accepted… But after many mistakes, I eventually have it right! I would never make a mistake if asked to type the hiragana for it, but the word reading is weird in this situation.
Well, with the ending being a particle it would not technically qualify as a single word. I think WaniKani makes a similar statement when I introduces the term as “vocabulary”.
I’m not sure anyone would analyze it as being two separate things at this point. (こんにち and は)
Setting aside how hard it is to define the concept of “words” in Japanese in the first place, こんにちは is a single entity that has etymological roots in being separate entities.
… and those etymological roots are what we have to bear in mind when we type the ‘reading’ in WaniKani. I certainly consider it a word in the ordinary sense of the word “word” and agree with what you are saying.