Gale would find some dangerous magical thing and poke it and end up dead.
Shadowheart would walk off a cliff giving the stink-eye to a porcupine that she thought was staring at her.
Lae-zel would have been eaten by Goblins or hung by the tieflings for being over-aggressive and arrogant.
Wyll - convinced of his own legend would take on the Goblins solo and end up eaten.
Astarion would end up dead trying to drink blood from some rando person or captured by his master or in service to another powerful entity who can protect him.
These aren't adventuring companions, they are people that need a life-assistant or they end up strangling themselves trying to put pants on!
dunno about Halsin in particular but you've just perfectly outlined why I don't like any of the current companions.