[megmogandog]

Where are you getting diminished 7th from? If you play the 3, the 5, the 7, and the 9 of E7 it's G# B D F#. At least in jazz we call that shape a "half-diminished" chord or "minor 7 flat 5", and it will stay that way no matter how you invert it or move the voices around between the hands. You'd only get a diminished seven if you flat the 9th to F natural (which actually often happens in jazz though not in the context presented).

The point I think you're missing is that the blog post isn't a music-theoretical presentation of what E7 is 'ontologically', it's a guide for what jazz pianists should play on that chord in an ensemble context. And in that context what's written here is very standard advice, since it's assumed the bassist will be playing the E. If there was no bassist, say if they were playing solo piano, a pianist will often play the E in the bass.

It's also clear from the way the article is written that they're already assuming some basic theoretical knowledge. It's never explained what notes are in an E7. If you don't know that, yes it will be confusing, but only because the article is not for you.

Overall I think the post would be very helpful for someone who knows the basics and is just getting starting playing with others.