You guys know me and that I never do this, but considering that using 今日は for こんにちは is normally avoided in the wild because convention has it reserved for きょうは and こんにちは is almost always spelled in kana…? There’s lots of nitpicking WK that goes on, but I never see anyone question this obvious point.
It’s used in things like 今日はご機嫌いかがですか, which is kind of a set phrase in a letter or something, though it’s obviously fairly stiff and people don’t write letters much anymore.
Also, the lesson already makes the points you made, so it’s not like they’re unaware.
Okay. Brought it up after seeing some WK user confused on the Reddit sub recently, and also see 今日は used a LOT in tweets, YouTube, etc in announcements for the today’s content.