Zero sounds like a normal young Akita with the rough play and
he is probably dog dominant if he does not back down.
Count your blessings he is not dog aggressive. (NOT fun)
Being neutered did not affect his dog aggression because
in his case I believe his aggression is genetic.
Neutering might have curbed his tendencies like humping,
and wanting to roaming etc.

Zero, must be a character to watch.
I use to love watching Sheba play with other dogs in her
younger days.
I bet the video of Zero is priceless.
The springer might not be a good idea, I guess it's back to jogging for you
on those COLD days with a warm coat. lol

Don't worry about writing about Zero. Us Akita people love hearing
other Akita stories.