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You can still start plain ED (at least I still have separate options in the Frontier launcher for ED, ED: Horizons and ED: Odyssey). But, if I remember correctly, the ED option just launches the Horizons client with all planetary landings disabled.there is no elite dangerous base game now. horizons IS the base game and there are not quests as such so there is no order you need to play the content in . in a way Odyssey is a good place to start (which is an extra paid expansion, has a little more content but higher minimum system requirements) as iirc there is an option to start without even owning a ship
But, I'd agree starting with plain ED is unnecssary - like you say there's no set order to play in and there's nothing in plain ED that you can't do in Horizons.
There would be advantages to starting with Odyssey, true - only needing to learn the new user interface for one. Depends on what price you can get both base game and DLC for, I guess.