So here is a little thought experiment you can do, to see just how disconnected odyssey is from the rest of ED.
So you are playing ED right now, i want you to think "How would the rest of ED be effected if i choose to completely ignore everything odyssey offers" So no more on foot, anything you do on foot, completely cut outta the game, what would that effect the rest of ED?
Now, i want you to do the same thing, but this time, imagine if you were playing ED, and you choose to ignore everything horizons brought to the table, and how that would effect the rest of ED.
When you think about that you realize that if you ignored all of horizons you loose out of engineering your ship, which vastly effects the rest of the way you play ED, it effects exploring, trading, definitely combat, mining, everything would be impacted if the features of horizon were just removed. By contrast, if you today removed everything in odyssey, nothing would change with the rest of ED.
This is what i mean when i say Odyssey is completely disconnected from the rest of ED, it does not blend anything well, it does not offer any integration to the rest of ED, its just a bolt on DLC, definitely by no means an expansion. As an expansion would imply that its adding on to the rest of the elite dangerous experience, but its not if you can completely ignore it and progress through the game just the same.