I'm not sure what to make of that first point.
You absolutely do NOT need to have an explicit grid when "vectors" can play the exact same role in a 3D environment.
The threaten condition is given within a certain distance from an enemy. Appears to use the 5e placeholder of 5 Feet. The problems are thus.
1) The game does not give you vector information for how far enemies are from a position your planning to move too. This requires eye balling it to avoid the status.
2) The 5ft range for this status is a holdover from a grid based system used in 5e. The rules intention is you are in range of enemies melee attacks thus must fire more carefully. 5 foot range is universal reach for nearly all melee weapons even daggers using a grid system. When you start breaking movement down beyond 5 feet squares and giving real weapon ranges, the simplified grid based rule doesn't work well.
3) It easier to eye the rough range of the weapons. But still be threatened by them when outside that range. This isn't intuitive.
Disadvantage isn't a weak status condition either.
