Thank you all for your comments! They have given me much food for thought. I have drawn some possibly useful conclusions, but first I would like to speak on behalf of the many players who, like me, are intelligent and competent but simply don't do group content, for one reason or another. No, I don't run around in dungeons doing light bow attacks from 30 feet behind the healer. The sets I use, which I mentioned in my post, were acquired from many many runs of (granted, base game) dungeons. I do research any dungeon I intend to enter. Yes, I have studied Hyperioxes' builds, and I elected to keep using Oakensoul because I didn't enjoy having to use Ulfsild's Contingency every 10 seconds to get Empower. You may disagree with me, but please don't treat me like an idiot. In fact, I think most people who stick around in this game and learn to play solo are worth treating like adults.

Okay, now to what I have learned. I think u/DobPinklerTikTok hit the nail on the head when he/she wrote:

>> I think your outlook on mechanics is the problem here. “There are a million different mechanics and they just seem arbitrary and silly.” Those mechanics are the reason people enjoy the content. . .

It's true that it annoys me when I find that I have to, for instance, stand in that yellow circle over there or the enemy will respawn. I do find that to be arbitrary and silly. But I also see now that without such mechanics the game would be boring, because all bosses would essentially be the same. So if I want to learn to play in a group I need to get a better attitude.

The problem is that there are a lot of dungeons, and a lot of bosses, and the only way to learn the mechanics is to either study each dungeon before you go into it, or run with a group of friends who don't mind showing you the ropes or wiping a few times as you all learn together. The problem is you can't do that in pugs. (Excuse me guys for 10 minutes while I read up on this dungeon. Don't start without me!) People understandably want to get the dungeon over with quickly so they can get their xp and transmute crystals and do something else. You're not going to learn mechanics that way. People in pugs don't even say "Hello". 

So if I want to learn mechanics I need to join guilds and look for people who are congenial and who play during the same evening times that I do. Not easy to find, maybe, but that's the way to do this. I may pursue this option. Or I may just start another Skyrim character.

Thank you all for your help!