You keep bringing up taxi flights. They only exist to allow you to cover large distances and are under control of the game makers.
You can still interact with the world, you 'll just have to interact with it for longer.
You are making valid points, I understand what you are saying, but the problem with flying is it removes too much content. Its not good to have the world being interacted with purely on the players terms dropping in and out of the game.
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Yes and limiting the player to controlled flight paths limits the time and areas a player can be inactive.