To be honest 807 pokemon is daunting for any newcomer. Obviously people are going to be turned off hearing that.
Should probably note that very rarely are you able to actually obtain all Pokemon at the start of a generation. For example, I recently had to have someone trade me a Glameow with its Hidden Ability (Keen Eye) because I need a Defiant Purugly for a Battle Spot Special team I'm making. As it turns out, Glameow is not even obtainable in gen 7, and the only gen 6 games where Glameow is catchable are on mirage isalnds in Omega Ruby and Alpha Sapphire, which don't even spawn every day!
This is probably why Gen 7 doesn't have a National Pokedex. Gamefreak's solution is more hiding obscure Pokemon away rather than deleting them. This way, they aren't required for completion, but fans of them (or in my case, needing it for a team lol) don't get burned either. I think this is a happy balance that seems to work!