Let's start with a dps number, 500k dps is easily achievable by most mapping builds when you take into account flasks, charges, other temporary buffs like Vaal haste etc
Let's assume it's pure elemental damage, meaning 20% reflected damage on a reflect rare.
This means 100k reflected damage.
How does the average build mitigate reflect? 75% resist, soul of yugul (25%), Ash frost and storm (10%), fortify. That's pretty standard right?
= 100 * 0.25 * 0.65 * 0.8
= 13k dps reflected or 87% reflect protection
Edit: reduced reflect damage taken is additive with fortify, not multiplicative, so it ends up at 11.5k dps reflected. Not 13k.
Average human reaction time for visual stimulus is around 0.25 seconds
In 0.25 seconds, you've just dealt 3.25k damage to yourself.
Most builds will be at around 6k life, so that's 0.46 seconds to move before you die to reflect damage alone
If you take leech into account, 1.2k per second without Vaal pact, 2.4k with Vaal pact, that is now 11.8k or 10.6k dps reflected
Meaning you'll die in 0.51 seconds without Vaal pact or 0.57 seconds with it.
Taking into account the average human reaction time being 0.25, you only have about 0.3 seconds to remove yourself from the reflect mob, hit your life flask, and somehow avoid all damage from every single other mob near you.
Your average movement skill is slower than that, meaning you'll be standing next to the reflect rare mob. You might not be reflecting damage to yourself because you stopped casting and used your movement skill, but you are still next to a rare mob and potentially a group of white/magic mobs. They will hit you.
Meaning that almost every reflect encounter is a near death experience. You have 0.3 seconds to survive. Multiply that across 1000 maps and hundreds of reflect rares and there will definitely be situations where you zone out, loose focus, your reaction time is a lot slower. You will die.
It is inevitable. You will die if you play a build that can hit with only 87% reflect protection. You will die.
Yes you can boost this higher through slayer and elementalist, but is it fair to force players to do that? Only 2 playable ascendancies for every build that can hit in 3.1?
You can also boost it through resist flasks, which gives you almost 90% reflect protection. That only gives you an additional 0.1 seconds or so to react. You'll still die eventually.
Yes there is also block and dodge, and to a lesser extent mind over mana as ways of stacking additional reflect protection, there is Sybil's lament too.
But my question being, should we have to invest into these things to counter a mechanic we come across once every 3 maps?
Look at freeze, flask. Bleed, also flask. Chaos damage, multiple ways to get immunity to it while still benefiting the user, such as pain attunment giving free damage, coruscating elixir providing a way to regen ES fast. Important thing here is that these give immunity to these mechanics. Not resistances to it. While also providing the user with benefits besides immunity/protection to the mechanic in question.
Reflect? Requires heaps of investment to survive the initial interaction with the mob as well as good reaction speed. Requires insane amounts of investment to actually be able to kill that mob safely.
Think it's about time we get a reflect immune flask. Or some sort of reflect immunity, not reduction. Reduction doesn't really do anything except give you another 0.1 second to look at your character while it inevitably dies.
Edit: one good suggestion was to change reflect to have a duration, and it acts like the thorns buff. This wouldn't invalidate reflect protection modifiers like an immunity flask would (such as elementalist), and still means reflect is something you have to play around. Interact with the map if you wanna call it that. Probably a better option than an immunity flask
Edit 2: the main flaw in this argument is that mobs will die long before you reflect enough damage onto yourself to kill yourself, because they don't have that much hp. At 500k dps, if you die in 0.5 seconds, that's a 250k health rare mob. Is that a reasonable amount of health for a rare mob? I don't know. There isn't any data on rare mob health .. anywhere. If there is I'd be happy to read through it and adjust my argument as necessary. But I'm fairly sure you'll come across mobs with way more than 250k life pretty commonly if you alch and go high tier maps, like 14+.