Am I missing something with the Target Lock control?

Maybe it’s user error but I feel like the target lock is extremely buggy or clunky.

I’m fighting Antumbra’s Sword and the hardest part of the fight is locating where the heck he is in the arena. I shouldn’t have to press target lock (which is bound to down on the D pad forcing me to take my finger off the left thumbstick) ten thousand times in a fight.

Am I missing something or is this just a fault of the game? Can I rebind it? It never seems to stay locked for more than one exchange.

Thanks in advance!