Lethal tempo is good for dps and extended fights, on the other hand, PTA is good for focusing down on high-priority targets.

But when facing tanks, Press the Attack is generally more effective than Lethal Tempo.

So it depends on the enemy composition; if they have tanks, you should go for PTA over LT.

Lastly, it also depends on your playstyle.

Dark harvest works well too but it's much better to get PTA & Sorcery rune setup because it synergies with this build and let you scale even stronger with gathering storm but if you're comfortable with DH it's still good, After the recent prowler's claw buffs yes its really good. I have tried it before the 13.16 patch which had a 10 second cooldown passive it was still strong, Now its much better that the cooldown reduced to 5 sec.

But the reason I build BT over it is because:

You already have 96% armor pen including your ult which your critical strikes get 50% armor pen. 18 lethality doesn't really impact that much compared to BT.

Bloodthirster gives you lots of lifesteal with the amount of ad you get from gathering storm and you will have more sustain. Not only that... Bloodthirst gives you a passive that gives you 10-40 and when you combine it with absolute focus it pairs really well! You'll get 58 bonus AD level 18 when above 70% plus gathering storm that'll give you even more dps and sustain.

You can still sell collector and replace it with prowler's claw after you get BT.