The evidence shows that Luther's back is invulnerable BUT his arms and head are not.

Here is a Luther survey, tv show evidence only:

1. (s01.e03) Knife wound to forearm in fight with Diego. Luther sustains a cut, our first glimpse of apeness.

   Image: https://mk0whereverilood1iwx.kinstacdn.com/wp-content/uploads/2019/02/Cast-and-Characters-Netflixs-The-Umbrella-Academy-Luther-Tom-Hopper.jpg

2. (s01.e03) Luther under chandelier. Chandelier falls entirely on his back and he just gets up. This freaks out Hazel.

3. (s02.e01) Apocalypse scene. Luther takes the tank shell to the back and flexes, apparently feeling the explosion, but unharmed.

   Image: https://www.thesun.co.uk/wp-content/uploads/2020/08/NINTCHDBPICT000600588702.jpg

4. (s02.e01) First boxing scene. Luther takes many punches to his front, but they appear to do minimal damage to the torso. Right hook bloodies his mouth.

5. (s02.e03) Second boxing scene. Luther throws the fight. Knocked out, presumably from the uppercut to the jaw. Next day (e04) has facial bruising and scabs.

6. (s02.e09) Luther and two Fives. Five kicks Luther in the crotch, who reacts as any (human) man would.

7. (s02.e10) Lila throws Luther through a wall head-first. Clearly dazed upon bellyflopping to the ground.

8. (s02.e10) Luther is shot. The first shot hits Luther in the head.

Shot 1: Blood spray from back of head. Whips his head back.

Shot 2: upper arm. Blood sprays forward.

The evidence shows his back is invulnerable, BUT his arms, although also affected by the ape-serum, can be pierced. I suggest that Luther's arms are less vulnerable than his head, because the Handler's bullet passes through (impales) his head but not his arm. (i.e. The blood exits the back of the head, but the front of the arm.)

The evidence shows that Luther's back is invulnerable BUT his arms and head are not.

Here is a Luther survey, TV show evidence only:

1. (s01.e03) Knife wound to forearm in fight with Diego. Luther sustains a cut, our first glimpse of apeness.

   

2. (s01.e03) Luther under chandelier. Chandelier falls entirely on his back and he just gets up. This freaks out Hazel.

3. (s02.e01) Apocalypse scene. Luther takes the tank shell to the back and flexes, apparently feeling the explosion, but unharmed.

   

4. (s02.e01) First boxing scene. Luther takes many punches to his front, but they appear to do minimal damage to the torso. Right hook bloodies his mouth.

5. (s02.e03) Second boxing scene. Luther throws the fight. Knocked out, presumably from the uppercut to the jaw. Next day (e04) has facial bruising and scabs.

6. (s02.e09) Luther and two Fives. Five kicks Luther in the crotch, who reacts as any (human) man would.

7. (s02.e10) Lila throws Luther through a wall head-first. Clearly dazed upon bellyflopping to the ground.

8. (s02.e10) Luther is shot. The first shot hits Luther in the head.

   Shot 1: Blood spray from back of head. Whips his head back.

   Shot 2: upper arm. Blood sprays forward.

   

The evidence shows his back is invulnerable, BUT his arms, although also affected by the ape-serum, can be pierced. I suggest that Luther's arms are less vulnerable than his head, because the Handler's bullet passes through (impales) his head but not his arm. (i.e. The blood exits the back of the head, but the front of the arm.)