If your primary team has no outlet for black, but generates it (like the very common Luke Cage/Iron Fist combo), going 5 on black makes a lot of sense. The defense tile will be good enough most of the time, and having two big damage powers and a stun is valuable.
If you already have a primary black outlet (3* Cyclops, Black Panther, Hulkbuster, etc.), having a 5 in red will really help against boosted enemies in PvE, especially ninjas and minor strike tile creators like Daken. You lose the stun, but you reduce health pack usage during grinds.
With 5/4/4, you end up in the middle - you could be stopping more damage or doing more damage, but there aren't very many regular opponents that warrant "just a little more defense" and "do less damage".
Here's the breakdown:
- Unbreakable - PASSIVE
With his bulletproof, steel-hard skin, Luke Cage is a walking tank. At the beginning of every turn, if there are no friendly Protect tiles on the board, Luke creates a strength 33 Protect tile.
Level 2: Creates a Strength 38 Protect tile.
Level 3: Creates a Strength 45 Protect tile.
Level 4: Creates a Strength 58 Protect tile.
Level 5: Creates a Strength 85 Protect tile.
Max Level: 3 - 141 Protect tile, 4 - 182 Protect tile, 5 - 268 Protect tile
- Jab, Jab, Cross - 6
Luke sets up for a classic one-two punch to knock his opponents cold. Luke deals 164 damage and places a 4-turn Countdown tile. While active, Jab, Jab, Cross deals 597 damage instead.
Level 2: Luke deals 190 damage or 710 damage if his Countdown tile exists.
Level 3: Luke deals 246 damage or 818 damage if his Countdown tile exists.
Level 4: If his Countdown tile exists, Luke also stuns the target for 1 turn.
Level 5: Luke deals 328 damage or 1367 damage if his Countdown tile exists.
Max Level: 3 - 783/2596 damage, 4 - 783/2596 damage + 1 turn stun, 5 - 1044/4340 damage +1 turn stun
At level 4 in red, you only gain 41 points of damage control at the expense of 261/1744 in black damage. On the flip side, you gain a one turn stun at the expense of 86 points of damage control.
I currently have a 5/5/3 Cage, but I don't really use him as much as I used to. I'm debating moving to a 5/3/5 build for when he's in Heroics and I need to slow down Ares or Juggernaut.
Having yellow at 5 means having a 10k nuke when he's boosted, so I don't see myself dropping below 5.
(gravel made some of my points, but I'm too lazy to change what I wrote.)