A game's realism is not determined by how close it is to real life, rather by how well it emulates real life.
TL;DR at the bottom.
Tarkov does a lot of shortcuts and emulation, from the way your inventory looks and is managed (you don't have squares in your backpack, do you?) all the way to movement, healing and shooting mechanics. Why can't we take some of these shortcuts to make the game more realistic and more enjoyable to run with a friend or two?
In real life your coworker, spouse or friend will be able to recognize you, generally, from dozens of meters away even if you have your back turned. In fact our brains are so amazing that we can even tell a person just by seeing a very minor part of their body, like their hands. So you're telling me that I cannot tell my friendly combatant from a few meters away in Tarkov? The reason this doesn't work in video games, like Tarkov, is because everyone has the same body and same stance, there are no subtle differences in posture, body type, etc.
That's why other games, many of them realistic (such as Squad and Insurgency: Sandstorm), compensate for that by adding some form of teammate indicators, even if minor. Even Arma has friendly indicators, so don't tell me that Squad, Insurgency and Arma are less realistic because of them, people who play them will beg to differ and would object to their removal.
Because Tarkov has RPG-elements it could fuse together so well. To determine how fast an indicator appears and at what distance could be determined by how many raid hours or raids you have with a particular person as well as your perception, intellect and memory. Maxing these skills could allow you to instantly get a friendly indicator when your teammate shows up from behind a corner, and that would be great since it would solve many frustrations people have with Tarkov.
And, no, indicators don't need to and probably shouldn't work through walls, floots and obstruction. The game already does multiple various scans for LoS and accounts for grass and bushes so this feature is already implemented, it can just be applied to friendly indicators, should they be added.
I know that some people reading the title and this post instantly got an exclamation mark above their head with the thought "but that would make teams OP and running solo be such a disadvantage!!"… that's true. To a degree. Playing against a team is still a disadvantage and always will be because Tarkov isn't meant to be fair, that's why you'll see people with millions of RUB worth of gear in the same raid as people with less than a hundred. Most experienced teams will have good enough comms that they'll still shoot you at a reflex level, especially if they're holding a position. But in the end, you're not at a disadvantage against a team because there might be some short-term chaos when the fight breaks out, rather it's because you're outnumbered and that has nothing to do with the team being able to tell each other apart (this sounds ridiculous just typing it) or not. In my opinion 5-man shouldn't even be a thing in this game, but that's a whole different point that has little to do with this post.
In real life you can tell your coworkers, friends, etc. from a hundred meters away even when their have their backs turned because our brains are very good at social recognition. This doesn't work natively in Tarkov because everyone has the exact same body, body type, posture, skin, etc. Tarkov should use some form of indicator that would represent how our brains work IRL. Other realistic games do this.