The experiences described are similar to mine. Keep in mind if you can see those fish, ten thousand other fisherman have thrown everything in their box at them in the past week.
If going small on the fly is not enough, go super small on the leader, too. I used to carry 2 pound leader with me for that situation on the blue ribbon wild trout water the Green River on the Wyoming/Utah border. Fishing pressure was horrendous, but it was catch and release and has something like 10,000 fish per mile. Those fish get caught and released so many times they literally don't fight when you do catch them, like they have learned that giving up gets them off the hook faster. Pods of 18" trout will feed right in front of you. They rise to the fly and sometimes even touch it without taking it in because they see some tiny thing that is off. Going super small on fly and leader will sometimes still catch a few of those.
I eventually gave up on that technique because it was not all that fun. Even on a 2 pound tippet an 18" fish was not much of a challenge to land because they would just roll over and swim with the line tension to come in. Instead, I started hiking into areas on the same river where there was less pressure and the fish were less educated. And they fought like crazy then, too.
Less educated fish are frequently nearby, but Iess visible. They might be feeding back under the willows where the average angler cannot make the cast, or under a pile of floating wood, or at the edge of an undercut bank. Look for places that the average angler doesn't think about or cannot really see, yet still offers a safe and easy feeding lane for the fish. Figure out what those spots look like and you'll be several steps ahead of the herd.
I remember as kids my younger brother decided to hand feed his line down stream with live grasshoppers on the hook. It was the only way he could thread his bait into the undercut banks and under the low hanging trees where he wanted to fish. My dad is not an angler, but drove him to the river and watched. Dad thought it was a wild goose chase, then was amazed by the results. At 13 years old my bro landed a limit of 16"- 23" wild brown trout that day. What was amazing is how many larger fish he broke off on the light line in the rocks and branches. He was only able to land one out of every 4 fish he was hooking. But boy did he have a great time. And it totally transformed how we both approached trout fishing. More imagination, and come up with techniques and places others don't think of.
Feeding his line on a down stream drift at the same speed as the water flow became one of his go to techniques as a kid, whether using bait or using a spinning rod to tuck a dry fly into a downstream pocket where the fish never see a hook. Now in his forties the guy is a dangerously effective angler. He takes his youngsters out and sets them up to catch monster wild trout. We all wish we had a dad like that when we were squirts.
On that note, I am starting to think the fishing obsession always skips a generation though. It did with my children. As adults they do like to join me once in a while, but none of them take it up in their own time. I have a covert plan in place to turn their children into wild eyed obsessed anglers as soon as they're big enough to hold a rod.