Pretty much all of this is spot on. My builds were both around 6' 200 lbs until last night. I made tiny players and the difference was so noticeable. At least doubled my points output and could play aggressively on the fore check or pinches, yet always seem able to recover my position.
The problem I feel like is that it is way too easy to play with the puck in close proximity to the opposition, because defending is incredibly dependent on User reaction time. Even the AI can't process the play with the speed puck carriers bare down on them with, and so it is no surprise User defenders are getting walked around as easily as the AI often is.
So far my only solution to the problem is to play the most sound, patient, positional brand of defense I can with a focus on NOT making plays on the puck until I am damn sure of it OR to join the meta. The former solution has lead to sequences where a User puck carrier will skate circles and perform loose puck dekes for a solid minute trying to get past me out of the corner. I can't get the puck off of him safely, but they can't get past me reliably so it just becomes a stalemate until others get involved (usually opening up a pass to the slot or backdoor, which was exactly what I was trying to make sure didn't happen). OR, join the meta.
Aren't competitive video games fun?