Deflection - Design

The Problem
Conceptually, deflection was meant to mitigate situation of getting one shot the moment your dodge doesn't roll.
It's not something new in ARPG as Diablo 3 had the exact same problem in it's time.
However, currently deflection is another layer of randomness that can't reach 100% chance, still leading to situation where bad roll of 2 dices will lead to getting one shot.

Possible solution
Instead, why not flip damage reduction formula from Armour?
Small hits would be reduced by next to nothing, while heavy hits that are likely to take your entire life would be mitigated the most.
This would compliment dodge that is great against many weak attacks, just like armor has it's own complimenting stat of "X% of Armour also applies to elemental damage".
Though with this change numerical values might be too good, so taking new deflection damage reductions to the power of 1.3 ( 10% becomes 5%, 40% becomes 30% ) would be easy nerf that keeps concept of "weak against small hits, strong against heavy hits".

Deflection is a pointless band-aid stat poorly designed.

It wasn't just because of the RNG of evasion. If was also because for some reason you have evade certain attacks, notable slam attacks. This is an inherently flaw in core design since attack Vs dodge are natural counterparts. Generally manipulated by accuracy, blind and similar effects.

If I were to design "Deflection" It would be a stat which takes incoming attack damage and converts into damage over 3 seconds. Say you have 500 Deflection and take 1500 damage. 500 of that would be over time. This is how you solve RNG stats like dodge without a mess.

Needless to say outside special attacks Evasion and this be for anything with the "Attack" tag.