OP I mean no offense, but you remind me of my beginning years as a gamer, where I would have this insecure mentality whenever I played any game where there was a player vs AI component. I would always toggle the settings to give myself the max resources/advantages because I was afraid the AI would rush me/get better stuff earlier than me/win before me etc. etc.
Eventually I learnt to let go and applied a competitive mindset to strategy gaming where I analysed what worked over the long term, what didn't, what really mattered etc. etc.
For example you mentioned
The overwhelming sensation I get now is that technology whizzes past at such an unbelievable rate (at least until modern onwards) that the problem is being overwhelmed with choices of what to build. Both buildings and units. And I would say that it IS stressful because you know that the AI is receiving enormous bonuses that allow it to build everything, it does not need to make the same opportunity costs.
The simple answer is to let go. Let go of those shiny dazzling Wonders and and focus on your fundamentals: explore, expand, exploit, exterminate.
Let me give an example in my most recent Deity game: I entered the renaissance era and started constructing Leaning Tower of Pisa. This was still during the expansion period of the game and I had 4 cities with 2 nearby spots that I was planning on settle before I was going to start building military. I had finished the Liberty tree by this time.
Now while I was building this wonder, 2 nearby AIs settled in those prime city locations, which more or less meant I was screwed out of 2 cities, boxed in with only 4 cities for the forseeable 100 turns.
I ended up finishing Leaning Tower, but you know what? I reloaded back to before I started building the wonder and built 2 settlers from my capital instead. I recognised that a Wonder is in no way as good as two productive extra cities, not by a long shot, and especially since I was getting a production bonus towards settlers because of Liberty. I missed out on the Leaning Tower but on my way to victory now I recognised that those two settlers gave me returns exceeding 10 times that of a wonder.
So in short: focus on building what matters. Science matters,Production matters, Gold matters. Most of the time military matters. Culture only matters in so far as getting the Guilds set up, or housing great works. Getting Hermitage and Broadcast Towers in your highest culture cities is good, but otherwise you don't need the most of those ampitheatres/opera houses/museums in other cities.
You don't need faith buildings unless it's part of your strategy.
You don't need to build food buildings if your happiness is tight. You don't need to build happiness if you have a good reserve of it either.
Focus on what matters. Civ is a zero-sum game. To
Win is the same as making the AI
Lose. When you capture
their Wonders, they become
yours. Play with a plan. Is my plan to build a spaceship? Then I have to scout out the AIs and figure out who's my closest competitor and neutralise them so they cannot compete. Is my plan a cultural victory? Then I do the same for the closest cultural competitor. I only grab the relevant wonders and focus everything I do on securing those victory conditions.
If you play with the intention of having the most number of cities with shiny stuff in them and most amount of needless buildings, you're going to lose, and that is what I suspect you of doing right now.