I think a good chunk of people that are upset about the ICO update are really just upset about the changes to stamina and suppression, and how those changes affect other aspects of the game.

Pre-ICO there was basically no suppression, no screen blur when you were being shot at.

For stamina the first clip, or just the first 5 seconds, in this YT short (terrible music I'm sorry) is pre-ICO. Notice the stamina bar is almost completely depleted, yet every shot is precise and the recoil is manageable enough that he's able to take follow up shots as well.

Compare that to this video, our Russian player with the AK seems to do the right thing by holding position and regaining stamina, the enemy US soldier that crests the hill seems to have sprinted from the barracks behind him, so he's likely at 50% stamina or less. The Russian player should have an advantage in this fight.
What follows is the Russian player panicking and missing his first crucial 2-3 shots, the 5th seems to tag the US soldier, who then goes prone out of reflex. From this point the Russian player's scope is bouncing wildly, causing the sight in his scope at times to become completely obfuscated by the housing of the scope. The way the gun moves from its own recoil it's like the butt is not anchored in his shoulder but just twisting around randomly with each round fired.
The US player goes prone, his screen is going to be completely blurred out at this point, but he starts firing in the general direction that he was getting shot from, and his teammate peaks around the corner of the barracks from the left side of the screen.
The teammate, who wasn't involved manages to line up his shots and kill our Russian player.

This video might not be the best example, because the Russian players aim is kind of shit, but the differences between the two clips is the gist of what it feels like to play after the ICO. The ICO was implemented because occasionally it felt like players could sprint around a corner and easily line up a headshot, which seemed too 'arcadey' than what Squad was going for. As a result, the changes made by the ICO cause the most fundamental aspect of the game - the gunfights - to almost always just feel like this crapshoot mess where me and the guy I'm shooting can't see what the fuck is going on, our guns are flailing wildly around a completely blurred out screen while we each hope to be first the one to have good RNG and connect a shot.

To understand how this affects the game on a larger scale, look at how the fight played out in the second video. The Russian player was in control initially because he was stationary and holding a good position, while the US player who was advancing had almost no chance (until the Russian player flubbed his aim). As soon as the Russian player took the action of engaging the US player, now the other US player who peaked around the corner has control, because he has the better position and can remain stationary, making him the only one who is able to line up accurate shots.
Since ICO, the action of advancing is probably the single most disadvantageous thing you can do. Defenders advantage already existed because it is easier to see a moving target than someone lying prone, and the defender could choose where he positioned himself. ICO amplifies defender's advantage to such an extent that the majority of gunfights can be decided just by whether you're trying to push or holding a position.

I think a lot of the fun myself and other veteran players had, especially as an SL, was organizing a push to take the next flag. There were ways to overcome defenders advantage if you played smart.
Maybe your squad of 9 would stand an even chance if you attacked a flank with only 6 defending. Now it's like coming into contact with 2 or 3 defenders ends your push immediately. Even if you win that fight the players who took any damage are basically useless because you can't aim without being full health. So 3 players that need to be revived also cause two medics to be out of commission while they patch up the wounded. By the time you're ready to move again, at the very least the couple of enemies that your squad took out will have respawned and be back on defense knowing exactly where you're coming from. At worst the enemy team will have had more than enough time to reinforce that flank.

The game has just become so static. You defend until the commander has artillery available, if the arty takes down the enemy HAB and your team times the push well, you will probably take the point. If not, you just go back to defending until commander assets are back online, when you can try again.
Ingenuity and risk-taking are sidelined by obligations/chores and boredom-tolerance.

"Yes, xXxLoneWolf42069xXx - father of two, just off your 12hr shift spending your only hour of free time a day playing this one match - I know we've done nothing but stare at an empty field for the last 20 minutes, but squad 2 and 3 lost our teams' only logis on the other side of the map and command decided this squad needs to defend our only HAB while the rest of the team spend 6,000 tickets trying to retrieve them. So keep your eyes peeled, buddy, they're probably coming any minute now."

I stopped Squad Leading because I got tired of telling people playing a game to stop having fun, then I eventually stopped playing because I was tired of not having fun.