anyone who judges game design off of 'realism' or anything pertaining to it is missing the point of video games. dying in 1-2 shots in real life isn't fun; dying in 1-2 shots in a video game isn't fun either. in fact dying in general by means outside your direct control isn't fun both in real life in video games.
when an engagement takes 4 seconds to end that gives both parties plenty of time to reassess their tactics, equipment and environment in order to outsmart the enemy and give themselves an edge. if the engagement takes 0.3 seconds because all the guns instakill then tactics, equipment and environment are no longer important and the gunfight has less depth. video games are an escape from real life and give you the ability to assert your dominance over enemies. but anyone can move their mouse to a pixel on the screen and press the mouse button twice. asserting your strategic dominance by making use of your equipment and environment to win an engagement is much more powerful and fulfilling then just popping someone in the head and watching them die.
there are plenty of games that prefer not to pride themselves on their unique gunplay. insurgency is one of those games. if you really want all your guns in the game to kill in 1-2 shots because its realistic and you want all 40 weapons to be functionally identical because they all kill in 1-2 shots because its realistic there are games like that.
actually the more you play insurgency you realize that like in real life, guns of different types do serve a purpose. time-to-kill and effectiveness of various weapons actually makes a difference in the split second you and your enemy can see each other, esp when considering where you end up shooting (leg shots dont kill fast, prone reduces profile but more likely that a shot that hits you will instantly kill you due to only vulnerable parts being visible). but yeah there isnt room for 40 different weapons, but there's room for at least 15-20 as evidenced by the game's armaments.
regardless, the main appeal/focus is the tenseness of combat - nobody can one-man-gun and outskill everyone else, and you can die at any moment if you're not paying attention to your teammates and your positioning. the tactics reassessment is basically frontloaded - if you forget up and dont consider things carefully you die the second you're out of cover. there's no time to reassess or reposition while under fire unless your enemy is stressed and not aiming well, or you've already decided ahead of time where you're going. equipment definitely matters as explosives and scopes definitely make a difference in how effectively you can take control of an area (by killing the enemy or forcing them to retreat).
its definitely fun, and i dont think you should keep making these blanket statements about what is/isnt good/fun. i dont think anyone will dispute your statement about death irl though.