The uselessness of muzzle attachments that aren’t silencers or flash hiders is the only thing that bothers me. Manual spotting is a feature and a good one, it allows you to warn your teammates about enemies you see but can’t engage. It also drops quickly after you lose sight, so is hardly overbearing.
In my experience, the majority of enemies I meet do not have a diamond over their head, far from it. I also often get surprised when rushing towards an enemy that has a diamond on the mini map by one that did not. Clearly the system is not as all encompassing as you describe.
But more importantly, this is a feature that is meant to be played around. If you’re going to straight up run between two points in the open, you are going to be seen. Being sneaky shouldn’t just be reserved for surprising enemies you’re about to engage, I usually try to avoid obvious lines of sight in all my movements so I don’t get spotted.
In reverse, I will manually spot everyone I can if I can’t engage them without confidence, and it can be glorious to spot someone, see two-three teammates move in and take them down. It feels like communicating and working as a team, and I think the game would be decidedly poorer without it.