You have to consider that you won't be able to make a full lethality build, so Prowler's Claw helps a lot to give you that bonus when you need to make a Chempunk Chainsword or other item.

With my example build you will achieve 89 of base lethality, which is a lot, but you'll probably have to replace one of these lethality items with another depending on the enemy team, so The Black Cleaver helps you reduce opponents' armor enough for your Lethality to cover everything, this makes pyke an excellent duelist, able to even kill a tank with these, being an extreme counter of Tahm Kench for example when you make Serpent's Fang.

In team fights is another story, it can be very beneficial for the team if Pyke manages to stun most of the enemy team with E + Flash or E + Prowler's Claw, making it easier for your team to do a lot of damage and then you kill they all with your R, but if you are precipitated and use your R on someone and he uses Flash, or Zhonya or another escape feature you will be minus one in Team Fight, so Pyke combo as well as characters with Croud Control in Area.

Note: IF YOU TAKE CROUD CONTROL YOU WILL DIE, THEN HAVE TENACITY IN RUNE, IF YOU HAVEN'T CLEANSE OR QUICKSILVER SASH DO NOT TAKE CC!