fast travel should unlock only after the gta 6 credits
The first playthrough should make us learn Leonida by moving through it. Roads, bridges, neighborhoods and distances become memorable because we use them repeatedly.
Fast travel is useful, but it changes the map into a menu. Once it is available, every inconvenient trip becomes a loading decision instead of part of the experience. For a replay or postgame, fine. During the story, keep us on the road.
Rockstar spends years building radio, traffic, weather and roadside events. Skipping all of that on day two would be an impressive way to miss the game we bought.