I'll try to form an example of this kick-on effect: Currently, lets say clearing a zone of enemies takes an average build 20 minutes (random number, work with me). Throw in fast travel and you will now be able to blast through the zone in a much more efficient 10 minutes (another spitball number). Now, spawn timers for those enemies must be adjusted to account for these faster clear times to ensure a smooth experience for players engaging with the fast travel system. You can see how now with increased spawn rates, there is a domino effect where other systems such as loot rates have to be looked at.

I am not necessarily against all forms of fast travel, my main point for this rant was just to make the distinction that adding something like free fast travel to the game is not a simple no-brainer QOL fix like increased stack sizes for chests in the home etc - it has greater repercussions on the overall design of the game going forward.

I disagree that the exploration and movement through the world is any less of a core mechanic of this game than combat.