the biggest cause of death in cf is the inability to exit a losing situation. Bloodthirst is the best way to restrict your ability to leave a situation both by denying you the ability to acuratly gauge if you are winning or losing and also by turning every single non village mob and player into a barrier.

If you wait for fatigue sure you drop the melee abilities of the rager but aside from the lack of mv regen their mobility is not hampered. If you fight a thirsting villager it is a lot easier to get mobs involved in the fight or to execute a hit and run tactic because you have more time to recover during the run due to the villagers reduced speed.

you say that it is relatively safe to thirst in art because of the underdark. Well I garuntee you that if you use that tactic as a villager against me i am acutly aware of what paths you are most likely to take to safety which makes them actually very not safe for you.

yes thirst gives you a lot of advantages when it comes to toe to toe fighting but as an opponent you should recognize that and adjust your tactics to take advantage of the inherent weaknesses that come with that advantage. It is just silly to consider something as dangerous to the user as it is to the one used against as being overpowered.