It seems to me that helmets are simply not worth the massive cost they require. So I went about to do some research and crunch what stats I could to feel this out. I'm working with a limited data set so this is not complete and I welcome discussion.
I've participated in 787 raids this wipe and I'm going to be leaning into those numbers a bit, which could be faulty or not representative of the wider average of Tarkov players.
Of those 787 raids I have died 400 times, leaving a 48% survival rate. I have worn a helmet in every single one of those raids I believe, except perhaps a handful at levels 1-5. Every single raid except for exactly one was solo.
I do not know how many of those 400 deaths were headshots. The game doesn't provide those stats. What it does provide is how many headshots I have dealt.
I have 1095 fatal hits that I've dealt. Of those fatal hits 398 were headshots. These stats include PMCs and Scavs. I'm not the most aggressive player and actively avoid PVP when doing quests. I also almost never kill Scavs any more, keeping them up as a warning system since I'm a solo player.
So exactly 36% of my kills were headshots. That number is likely lower for PMC kills as it's much easier to headshot Scavs which remain stationary in the open at times.
If I assume that 36% is in the ballpark of an average player, then 36% of a player's deaths would be headshots. So let's say it's 36 out of 100.
Now, let's assume you were just wearing the Soviet army helmet which is around 22k. I wore that for about half of the wipe pretty exclusively. If we're talking about a player having to buy a new Soviet helmet after each death, and we're using that 100 death count as a baseline, that's 2.2 million roubles.
Now, let's assume the average loadout cost I ran was 300K. That seems in the ballpark as level 4 armor would be 50-80K, Soviet helmet 22k, Comtacs 22k, a 100k on average weapon (including silencer, optic, foregrip, 100k may be even a little low), two nades at 25k, a 15k backpack, and 50k on ammo. You could of course spend much more on ammo but lets assume you've unlocked all of the traders and are spending somewhere around 500-750 a round and only carrying two spare mags or so.
Ok, it's starting to get interesting. Of 36 assumed headshot deaths, let's say the helmet would save you from ricochet 8% of the time. I cannot find a solid number on what the ricochet chances are, but I've seen 4-8% tossed around for high chance ricochet helmets. I'm leaning towards a high number here since my position I'm trying to prove is that helmets are not worth it – so I'm being generous to the opposite argument to illustrate the point.
So a helmet ricochet alone would save you from 2.88 deaths. Lets round up to 3 because you were lucky.
How many times would it save you from a direct hit? This is very hard to calculate. Not often based on my experience. Sure, it would from an occasional Scav shot, but most often that's head/eyes anyway. Let's say it saves you from an additional 3. That seems somewhat fair. I'm welcome to an argument here.
This means that you were saved 6 times out of your 100 headshot deaths from wearing a helmet. That very roughly jives with my own experience with the game. It's certainly less than 10%.
So it saved the cost of six loadouts, at 300k each. That's 1.8 million. But you paid 2.2 million for the helmets over that span.
Now, you can say that you spend more than 300k on a loadout, which is fair and it would mean it saved you more roubles for those six lives. But you also probably aren't wearing the army helmet if you're spending half a mill on your loadout. If you switch to even say the 6B43 helmet at 33k per then you spent 3.3 million on helmets. I bet you're wearing helmets approaching 100k though. I know we didn't include visors here but I'd bet the math proposition is even worse if you include those, particularly since they don't protect you from decent rounds.
Of course if you find helmets on enemies and just toss those on it changes everything, particularly since they're not FIR and you can't sell them on the Flea. But that doesn't change the fact that someone bought that helmet and they probably shouldn't have from a pure economic standpoint.
If you're just chasing the high of winning a combat and don't care particularly about the money, then none of this matters of course. I can't imagine a world though where you somehow justify the cost of an Airframe from a value standpoint.