LDG-Gaming

Should have been dead though, if it really was fully charged

Only case I can think of that would ever produce 5 seconds is being melee'd at full power in the back, in which case, gg, you should die. I'm assuming that wasn't the case though.

Might have been survivable if attacker was being debuffed by proton pack? I don't know numbers.

Displacement is calculated based on net damage. Damage out -> Game Rules (proton pack) -> Player TakeDamage -> BallisticWeapon AdjustWeaponDamage.

Situation was thus: MRS138 melee from front, approximately 140 - 160 damage, displacement of five seconds. I assumed the weapon was fully charged because of the damage and displacement, but I could be wrong.

Melee displacement from CYLO UAW and CYLO FS is also having lot of time displacement cause you can charge them ... also melee movement is a bit faster than when you have a weapon, when you get hit, there is no escape because the melee user is always faster than the weapon user. With the first hit, you are displaced and jumping, dodging around trying to avoid the attacker... when the attacker is skilled, he can change to a weapon and spam you, or just keep displacing you until you are dead... In narrow places, there is nothing to do...
Best example is Horror, he charges you with melee from Cylo FS, and then finishes you with 1, 2 shots... and you may try to escape but his movement skill is quite developed...

Vs melee user with better movement skill than yourself:

Equip SAR / AM67 and flash him.
Equip any shotgun and kill him.
Equip bloodhound and tase him to death.
Back yourself up with M46 fields and draw him in.
Use MARS cryo grenades to slow him and kill him.

There's an assload of strong melee responses in the arsenal.

Add to that list "block him", repeatedly hitting block will slow melee attacks down

Or alternatively, hold circle and use the left analog stick to use CQC against your opponent.

But seriously, I can't stress enough the basic backwards jump wall-dodge jump. Learn it. Embrace it. Relish in it.