Flee is too generous. Any fight gets hard? Guess I'll flee!
If an ability trivializes a large portion of the game, it probably needs to get modified. This is the case with flee. It's the solution to every combat that is going poorly. No downsides. 100% availability too.
It being so dominant reduces the viability of other methods of handling a fight.
Healing? Nah, just flee when you get low, bedroll, and rejoin the fight.
Tactical retreat? Nah, just flee, to get out. Don't waste the resources.
etc.
It shapes the game in a negative way to have an unchecked mechanic, especially if it's supposedly working as intended.
The onus of game balance shouldn't be on the player to have to tell themselves not to use core features that are too strong, it should just be balanced to be more in-line with a fun game design.
