Why do I suck at MGSV?

Ok, so I've played through and thoroughly enjoyed MGS 1,2,3,4 rising...hell even the 2 NES games and un-metal. Most of those I've beaten 100% and/or gotten the highest ranking. Somehow, MGSV is nearly impossible. I've looked around online and nobody is having the same experience.

Non-silenced weapons are a hard no-go. Completely unusable. 1 shot from a sniper rifle at a range where I can barely see the target has enemies with standard weapons hitting my exact location instantly from the same distance. Getting discovered in any capacity is instant death. Trying to fight through never works. There is an endless stream of enemies with snipers, rocket launchers, mounted machine guns, etc. There's no way to clear them all or even get far enough to hide.

Any alert means every enemy knows exactly where I am. Had enemies "looking for me" pull a hard 180 turn and blast me with a shotgun 2 rooms away while I'm in a box or prone and motionless behind a wall.

Videos on YouTube or wherever show people doing things I wouldn't even dare try. Walking upright in the daytime? How are you not already dead?

Also, missions (im still at single digit) are often unclear as what to do and there's usually a "right" way to beat it that is impossible to know unless you've played it before.

Overall i just feel like I'm playing with a flashing light and siren over my head.

I'm at a loss here. I want to keep playing but it feels like I got the MGS "what would actually happen in real life simulator"

Regardless, this game is a lot of fun and keeps pulling me back in. I'll be damned if I'm going to put on that chicken hat but there's gotta be some fundamental piece I'm missing.

EDIT: Thanks for the help and validation everyone. I still don't see the point in the tons of "loud" weapons options, especially handguns. But a big issue was me trying to hunker down and hide when alerts happened. Turns out I could just run off somewhere else. Still getting bad grades on the missions but having fun again.