If "Steam users" (=younger audiences, indie audiences) would be a commercial target:
A. Tutorial - just a few, short missions, learning controls ('start', landing', 'flying through rings', 'how to read instruments', 'how to deploy weapons') - a link to the already existing YT channel and videos would be enough?
B. Short Campaign - not more than just a bit of 'story' text & pictures between 'missions'. 'Missions' do not have to be more than a series of waypoints. the kind Ace Combat does. KISS² = Keep it Simple... & Short. A few hours of gameplay for the 10-15USD audience pocket?
C. Steam users will cry for "multiplayer" - it is unavoidable. Ignore? This is the most vocal crowd. They would generate more money on initial sale, but to double the work just to implement network code for those people, not to mention having to offer & maintain a server (or rather 'three' = US, Asia, Europe), etc - just for them, who will run away after 1-2 weeks to the next new shiny thing - I cannot see the value to justify the higher workload for a 'one-man-team'. But it is not up to me, to judge.
D. Full Gamepad support (menu) - for a potential console release, later? More pain now, big payoff later?
These suggestions are not 'yet another user's wishlist of features'. It's your game - not mine.
It is just one opinion on how to shape the game for selling it, or rather encouragement to find the wider audience and market window on the "Steam"-platform and/or XBOX/PS4 console release. Dev probably knows this way better than me.
There are already complex features implemented in these builds that go beyond a 'simple game', which thrills me, but may not match the kind of audience mentioned above.
I am saying nothing new here and to quote a famous American Philosoper: "Not every game is for everyone" (Shane Bettenhausen, Sony).