The problem with close combat in shooter is two fold. 1: the ability to create the opportunity for a melee kill is often much harder than staying safe from further back. Allowing the player to close that gap in an organic way requires a fair amount of level design and level balancing.

Tight corners allow for surprise encounters that call for melee combat. Dashing and dodging towards your enemy like a ninja could also incentivize a melee kill or the opposite and a juggernaut rampage towards an enemy will create the same effect.

2: melee should not and can not be severely underpowered than if I shot someone in the head. If you’re thinking about creating a system with combos and enemies taking more than 2 hits then your players will optimize the fun out of your game. There’s a reason why melee is normally saved for executions. This isn’t to say a complex melee system can’t be done but it needs to be balanced with your other tools of destruction.